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The Fragrance of Ambergris
... Solvent extracts of ambergris, which is a natural product of the sperm whale, but which is also found as jetsam on beaches from around the globe, comprise mainly a tricyclic alcohol ambrein (I, Figure 1), plus variable proportions of fecal steroids (Lederer et al. 1946;Lederer, 1949;Baynes-Cope, 1962;Rowland and Sutton, 2017;Rowland, Sutton, Belt et al. 2018;. However, ambrein is odorless and the characteristic odors of ambergris long valued in perfumery (Dugan 2011;Brito et al. 2016;Serra 2013) are in fact due to oxidation products of ambrein (Ohloff et al. 1977;Ohloff 1982). The presence of the latter has been reported in ambergris tinctures (viz: aged solutions in ethanol; Anon 1976) following steam distillation (Mookherjee and Patel 1977;Awano et al. 2005) but not, as far as we are aware, in samples of jetsam ambergris. ...
... SPME inherently extracts the more organoleptically important components of ambergris, which can be lost during solvent extraction and pre-concentration. Both pristane (Lederer 1949) and c-dihydroionone (Ohloff 1982;Schaefer 2014) have been reported previously to be components in ambergris samples of unknown provenance (Mookherjee and Patel 1977;Awano et al. 2005), where they represented (1% of extracts of distillates of ethanolic tinctures. No quantitative assessment was made in this study, but no doubt they were also very minor components of the present samples. ...
... The odorous constituents of jetsam ambergris are thought to arise from photo-oxidation and/or autooxidation of ambrein, with scission at the trisubstituted double bond, producing essentially monocyclic and bi-or tricyclic moieties (Ohloff et al. 1977;Ohloff 1982;reviewed by Serra 2013;Rowland, Payne, and Sutton 2018). The majority of the components identified herein in the SPME fractions including ambreinolide, AmbroxV R , the dihydroionones and c-homocyclogeranyl chloride, are likely explained by an origin from such natural processes. ...
We studied the volatiles and semi-volatiles of jetsam ambergris by solid phase micro extraction (SPME). They ranged from a black, sticky material from New Zealand, likely recently ejected from a sperm whale, to a white solid found on a beach in Chile and radiocarbon-dated previously to be about 1000 years old. The traces of volatile/semi-volatile compounds collected by SPME were identified by gas chromatography-mass spectrometry (GC-MS). These included odorous γ-dihydroionone and odor-free pristane as the major constituents. The ratios of these to one another varied, depending on sample colour and age.
... In our global fungal genome mining study, we discovered three types of onoceroids, which are triterpenoids synthesized from squalene or oxidosqualene through cyclization at both ends of the prenyl chain. Onoceroids have been isolated from bacteria 52 , ferns 53 , higher plants 54,55 , and animals 56 . However, to the best of our knowledge, onoceroids have never been isolated from fungi. ...
Genomics-guided methodologies have revolutionized the discovery of natural products. However, a major challenge in the field of genome mining is determining how to selectively extract biosynthetic gene clusters (BGCs) for untapped natural products from numerous available genome sequences. In this study, we developed a fungal genome mining tool that extracts BGCs encoding enzymes that lack a detectable protein domain (i.e., domainless enzymes) and are not recognized as biosynthetic proteins by existing bioinformatic tools. We searched for BGCs encoding a homologue of Pyr4-family terpene cyclases, which are representative examples of apparently domainless enzymes, in approximately 2000 fungal genomes and discovered several BGCs with unique features. The subsequent characterization of selected BGCs led to the discovery of fungal onoceroid triterpenoids and unprecedented onoceroid synthases. Furthermore, in addition to the onoceroids, a previously unreported sesquiterpene hydroquinone, of which the biosynthesis involves a Pyr4-family terpene cyclase, was obtained. Our genome mining tool has broad applicability in fungal genome mining and can serve as a beneficial platform for accessing diverse, unexploited natural products.
... These, plus trace amounts of zinc, aluminium and nickel, were reported by Baynes-Cope [9] for 'body' ambergris (a term for ambergris found in whale carcasses which was defined by Clarke [2]). Lederer [8] thought that the copper might catalyse photo-and/or auto-degradation of ambrein to the odourous components valued by the perfumery industry; a suggestion repeated by Ohloff et al. [10] and Ohloff [11]. Much later, Rowland et al. [12] used 5, 10, 15, 20-tetraphenyl-21H, 23H-porphine copper (II) to catalyse photo-oxidation of ambrein in water, since porphines (protoporpyhrin IX and mesoporphyrin IX) had been detected in ambergris in early studies [13,14]. ...
... Onoceroids have been isolated from bacteria, 34 ferns, 35 higher plants, 36 and animals. 37 However, to the best of our knowledge, onoceroids have never been isolated from fungi. Thus, the present study provides the first examples of fungal onoceroids and their biosynthetic pathways. ...
Genomics-guided methodologies have been widely adopted and proven beneficial for the discovery of natural products. However, a major challenge in the field of genome mining is determining how to selectively extract biosynthetic gene clusters (BGCs) for untapped natural products from a substantial number of available genome sequences. In this study, we developed a fungal genome mining pipeline that extracts BGCs encoding enzymes that lack a detectable protein domain and are not recognized as biosynthetic proteins by existing bioinformatic tools. We searched for BGCs encoding a homologue of Pyr4-family terpene cyclases, which are representative examples of domainless enzymes, in approximately 2,000 fungal genomes and discovered several BGCs with unique features. The subsequent characterization of these BGCs led to the discovery of the first fungal onoceroid triterpenoids and unprecedented onoceroid synthases. Our genome mining pipeline has broad applicability in fungal genome mining and can serve as a beneficial tool for accessing diverse, unexploited natural products.
... Ambergris, a natural perfume ingredient, is a waxy substance secreted by the digestive tract of male sperm whales and the best-known amber odorant natural ingredient [1][2][3] . Ambergris has been particularly used in the perfume industry for its intense fragrance and unequaled fixative properties 4 . ...
Sclareol, an antifungal specialized metabolite produced by clary sage, Salvia sclarea, is the starting plant natural molecule used for the hemisynthesis of the perfume ingredient ambroxide. Sclareol is mainly produced in clary sage flower calyces; however, the cellular localization of the sclareol biosynthesis remains unknown. To elucidate the site of sclareol biosynthesis, we analyzed its spatial distribution in the clary sage calyx epidermis using laser desorption/ionization mass spectrometry imaging (LDI-FTICR-MSI) and investigated the expression profile of sclareol biosynthesis genes in isolated glandular trichomes (GTs). We showed that sclareol specifically accumulates in GTs' gland cells in which sclareol biosynthesis genes are strongly expressed. We next isolated a glabrous beardless mutant and demonstrate that more than 90% of the sclareol is produced by the large capitate GTs. Feeding experiments, using 1-13C-glucose, and specific enzyme inhibitors further revealed that the methylerythritol-phosphate (MEP) biosynthetic pathway is the main source of isopentenyl diphosphate (IPP) precursor used for the biosynthesis of sclareol. Our findings demonstrate that sclareol is an MEP-derived diterpene produced by large capitate GTs in clary sage emphasing the role of GTs as biofactories dedicated to the production of specialized metabolites.
... (−)-Ambrox represents one of the most sought-after fragrances for perfumery. Its natural precursor, the triterpenoid (+)-ambrein can be found in nature as the main component of ambergris, a very rarely occurring coprolite from the sperm whale (Ohloff, 1982). Upon exposure to sunlight, (+)-ambrein undergoes photo-oxidation and (−)ambrox and related compounds are formed, a process that can also be simulated under laboratory conditions (Rowland, Sutton, & Payne, 2018;Sell, 2006). ...
The triterpenoid (+)‐ambrein is the major component of ambergris, a coprolite of the sperm whale that only very rarely can be found on shores. Upon oxidative degradation of (+)‐ambrein, several fragrance molecules are formed, amongst them (‐)‐ambrox, one of the highest‐valued compounds in perfume industry. In order to generate a Saccharomyces cerevisiae whole‐cell biocatalyst for the production of (+)‐ambrein, intracellular supply of the squalene, was enhanced by overexpression of two central enzymes in the mevalonate and sterol biosynthesis pathway, namely the N‐terminally truncated 3‐hydroxy‐3‐methylglutaryl‐CoA reductase 1 (tHMG) and the squalene synthase (ERG9). In addition, another key enzyme in sterol biosynthesis, squalene epoxidase (ERG1) was inhibited by an experimentally‐defined amount of the inhibitor terbinafine in order to reduce flux of squalene towards ergosterol biosynthesis while retaining sufficient activity to maintain cell viability and growth. Heterologous expression of a promiscuous variant of Bacillus megaterium tetraprenyl‐β‐curcumene cyclase (BmeTC‐D373C) which has been shown to be able to catalyze the conversion of squalene to 3‐deoxyachillol and then further to (+)‐ambrein resulted in production of these triterpenoids in S. cerevisiae for the first time. Triterpenoid yields are comparable to the best microbial production chassis described in literature so far, the methylotrophic yeast Pichia pastoris. Consequently, we discuss similarities and differences of these two yeast species when applied for whole‐cell (+)‐ambrein production.
... The triterpenoid (+)-ambrein is a major component of ambergris, an intestinal excretion of the sperm whale that represents one of the most valuable animal resources for perfume production. Apart from (+)-ambrein, ambergris also contains several cholestenol-type sterols (Ohloff, 1982). Upon exposure to sea water, sun light and air, (+)-ambrein undergoes oxidative degradation, yielding (-)-ambrox and several other odor-active compounds (Sell, 2006). ...
The triterpenoid (+)-ambrein is a natural precursor for (-)-ambrox, which constitutes one of the most sought-after fragrances and fixatives for the perfume industry. (+)-Ambrein is a major component of ambergris, an intestinal excretion of sperm whales that is found only serendipitously. Thus, the demand for (-)-ambrox is currently mainly met by chemical synthesis. A recent study described for the first time the applicability of an enzyme cascade consisting of two terpene cyclases, namely squalene-hopene cyclase from Alicyclobacillus acidocaldarius (AaSHC D377C) and tetraprenyl-β-curcumene cyclase from Bacillus megaterium (BmeTC) for in vitro (+)-ambrein production starting from squalene. Yeasts, such as Pichia pastoris, are natural producers of squalene and have already been shown in the past to be excellent hosts for the biosynthesis of hydrophobic compounds such as terpenoids. By targeting a central enzyme in the sterol biosynthesis pathway, squalene epoxidase Erg1, intracellular squalene levels in P. pastoris could be strongly enhanced. Heterologous expression of AaSHC D377C and BmeTC and, particularly, development of suitable methods to analyze all products of the engineered strain provided conclusive evidence of whole-cell (+)-ambrein production. Engineering of BmeTC led to a remarkable one-enzyme system that was by far superior to the cascade, thereby increasing (+)-ambrein levels approximately 7-fold in shake flask cultivation. Finally, upscaling to 5 L bioreactor yielded more than 100 mg L⁻¹ of (+)-ambrein, demonstrating that metabolically engineered yeast P. pastoris represents a valuable, whole-cell system for high-level production of (+)-ambrein.
Ambrox, a highly prized and commercially significant component of ambergris, finds widespread application in perfumery, cigarettes, cosmetics, and the food industry. Despite considerable attention to this research area over the years, an environmentally friendly and practical method for synthesizing (−)‐ambrox has remained elusive. This study presents a succinct and efficient approach to (−)‐ambrox synthesis, involving two consecutive alkylations at C‐6, followed by an acid‐catalyzed cyclization to give bicyclic ketones starting from (R)‐carvone. Subsequent reduction, Barton Vinyl Iodide synthesis, alkylation, and an acid‐catalyzed cyclization collectively achieved the synthesis of (−)‐ambrox with a satisfactory yield of 26.2 %.
(-)-Ambrox, the most prominent olfactive component of ambergris is one of the most widely used biodegradable fragrance ingredients. Traditionally it is produced from the diterpene sclareol, modified and cyclized into (-)-ambrox by classical chemistry steps. The availability of the new feedstock (E)-β-farnesene produced by fermentation opened new pathways to (E,E)-homofarnesol as a precursor to (-)-ambrox. Combining chemical transformation of (E)-β-farnesene to (E,E)-homofarnesol and its enzymatic cyclization at the industrial scale to (-)-ambrox with an engineered squalene hopene cyclase illustrates the potential of biotechnology for a more sustainable process, thus meeting the increasing consumers' demand for sustainably produced high quality perfumery and consumer goods. This review traces back to the origin of ambergris and the search for the source of its mysterious odor, leading to the discovery of (-)-ambrox as its main olfactive principle. It discusses the plethora of ways explored for its synthesis from diverse starting materials and presents the development of a process with significantly improved carbon efficiency for the industrial production of (-)-ambrox as 100% renewable Ambrofix.
Ambreinolide is a natural terpenoid with great value for perfume industry and natural product synthesis. Herein we report a novel total synthesis of ambreinolide on multigram-scale that employs a regio- and diastereoselective, high yielding, proton-initiated polyene cyclization using a catalyst easily generated in situ. Molecular structures were unambiguously confirmed by X-ray crystallography.
Ambergris, a sperm whale metabolite, has long been used as a fragrance and traditional medication, but it is now rarely available. The odor components of ambergris result from the photooxidative degradation of the major component, ambrein. The pharmacological activities of ambergris have also been attributed to ambrein. However, efficient production of ambrein and odor compounds has not been achieved. Here, we constructed a system for the synthesis of ambrein and odor components. First, we created a new triterpene synthase, “ambrein synthase,” for mass production of ambrein by redesigning a bacterial enzyme. The ambrein yields were approximately 20 times greater than those reported previously. Next, an efficient photooxidative conversion system from ambrein to a range of volatiles of ambergris was established. The yield of volatiles was 8–15%. Finally, two biological activities, promotion of osteoclast differentiation and prevention of amyloid β-induced apoptosis, were discovered using the synthesized ambrein.
Jetsam ambergris, found washed ashore on beaches, is an environmentally modified form of a natural product of Sperm whales which sometimes develops a pleasant odour. Odorous samples have proved valuable in perfumery. Identification of jetsam ambergris by analysis of organic-soluble extracts by Fourier transform infra-red spectroscopy (FTIR) and of derivatised samples by gas chromatography-mass spectrometry (GC-MS) has already been shown. Here, we describe a different method, in which characteristic alkenic protons and carbon atoms of the major constituent ambrein, were identified in whole extracts using nuclear magnetic resonance spectroscopy (NMR). The advantages of employing NMR spectroscopy included rapidity, reduced losses of volatiles compared to GC-MS and detection of non-GC amenable constituents. However, the identities and quantities of co-occurring individual components (e.g. steroids) could not easily be assigned in the unfractionated extracts by NMR spectroscopy, whereas they were by GC-MS, so an approach combining FTIR, GC-MS and NMR spectroscopic methods is advocated.
This chapter begins with a discussion on volatile organic compounds. Terpenoids, shikimates and polyketides provide us with most of nature's scents. Volatile terpenoids are important as natural chemical signals, and have also reached prominence in the flavour and fragrance industry; hemiterpenoids, monoterpenoids and sesquiterpenoids are discussed in detail in the chapter. The three groups of terpenoid degradation products that are most important in terms of odorous materials are those of carotenoids, ambreine and iripallidal. Shikimates are one of the largest groups of natural odorants; their biosynthesis is outlined in the chapter. Humans not only use plant odorants to find food and to assess its quality, but also use them for aesthetic purposes and perfumery. Fruits are well known for their lipid-derived volatiles and many also contain carotenoid degradation products. The chapter also discusses malodours Including human sweat malodour.
Onoceroids are a group of triterpenes biosynthesized from squalene or dioxidosqualene by cyclization from both termini. We previously identified a bifunctional triterpene/sesquarterpene cyclase (TC) that constructs a tetracyclic scaffold from tetraprenyl-β-curcumene (C35 ) but a bicyclic scaffold from squalene (C30 ) in the first reaction. TC also accepts the bicyclic intermediate as a substrate and generates tetracyclic and pentacyclic onoceroids in the second reaction. In this study, we analyzed the catalytic mechanism of an onoceroid synthase by using mutated enzymes. TC(Y167A) produced an unnatural tricyclic triterpenol, but TC(Y167L) , TC(Y167F) , and TC(Y167W) formed small quantities of tricyclic compounds, which suggested that the bulk size at Y167 contributed to termination of the cyclization of squalene at the bicyclic step. Our findings provide insight into the unique catalytic mechanism of TC, which triggers different cyclization modes depending on the substrate. These findings may facilitate the large-scale production of an onoceroid for which natural sources are limited.
When discussing highlights in synthetic chemistry with regard to usefulness in perfumery, we have to keep in mind that until the end of the last century, only natural ingredients were available for mixing fragrances. Since then, synthetic efforts to produce high-quality perfumes became more and more reliable. This is not the place to evoke all the interesting compounds created by the chemists’ fantasy and their knowledge concerning the feasibility of transferring laboratory procedures to industrially applicable ones; but we would like to look at the development of new raw materials and at improvements realized in the synthesis of known fragrant molecules to produce them more economically.
Die Grundlage der Kommunikation auf dem Gebiet der Olfaktion bildet eine wissenschaftlich fundierte Geruchsterminologie. Naturwissenschaftler befinden sich hier in einer schwierigen Lage, denn es existiert keine objektive Methode zur Aufstellung eines Riechkodex. Das Erkennen und Charakterisieren von Geruchsnoten ist ein psychophysikalischer sprich subjektiver Vorgang, der nach 2 unterschiedlichen Methoden erfolgen kann. Entweder wird die qualitative Beschreibung eines Geruchsmusters durch direkten Vergleich mit einer Serie von Referenzverbindungen als Duftmodelle oder mittels semantischer Methoden vorgenommen. Beide Verfahren erzeugen multidimensionale Profile (scaling) (quality space), die durch eine zweidimensionale graphische Darstellung geordnet werden können. Das Profil hängt von den ausgewählten Referenzmustern oder den semantisch ermittelten Deskriptoren ab.
Sensorisch aktive Stoffe müssen bestimmte molekulare Voraussetzungen erfüllen. Oberflächenaktivität, niedrige Polarität und ein Minimum an Wasserlöslichkeit werden vom Stimulus ebenso verlangt wie hoher Dampfdruck und starke Lipoidlöslichkeit. 294 ist das höchste Molekulargewicht eines Riechstoffs, gemessen an einem Labdanderivat [1]. Die chemische Reaktivität eines Moleküls bildet keine Voraussetzung für seine Riechstoffeigenschaften. Ein schwach polarer und ein stark hydrophober Molekülteil genügen zur Auslösung der sensorischen Aktivität. Seiner früh erkannten Bedeutung wegen hat man den polaren Anteil als osmophore Gruppe bezeichnet [2]. Es handelt sich dabei um funktionelle Gruppen, wie etwa Carbonyl-, Ester-, Hydroxyl- und Alkoxy-Reste sowie eine begrenzte Auswahl heteroatomarer Analoga.
Terpenkohlenwasserstoffe, in fast allen etherischen Ölen als biogene Komponenten vorhanden, besitzen nur geringe Riechstoffeigenschaften. Wegen ihrer extrem hohen Lipophilie sowie oft uncharakteristischen oder störenden Geruchsnoten werden ihre Vertreter in den meisten Fällen mit Hilfe physikalischer Methoden eliminiert und damit von der Parfümerie ausgeschlossen. Allerdings stellt diese Verbindungsklasse ein ideales Ausgangsmaterial zur Herstellung naturidentischer Duftstoffe dar. Ihre hohe chemische Reaktivitätführt außerdem leicht zu sauerstoffhaltigen Derivaten, die ein von natürlichen Vorbildern abweichendes sensorisches Verhalten auslösen und in ihrer unbegrenzten Vielfalt die Palette der Riechstoffe bereichern.
The use of biomimetic polycyclization with artificial cyclase is the most ideal chemical method for the synthesis of these polycyclic terpenoid. This chapter discusses the biosynthesis of polycyclic terpenoids, biomimetic stereoselective polyene cyclization induced by artificial cyclases, and total synthesis of bioactive natural products using stereoselective polyene cyclization as a key step. Enantio- and diastereoselective polyene cyclization reactions promoted by small-molecule artificial enzymes have been developed as key steps for the practical synthesis of polycyclicterpenoids based on biosynthetic pathways. The chapter overviews recent progress on the stereoselectivepolyene cyclizations. There have been no successful examples of the polyene cyclization via a chair–boat transition state likesterol folding. MacMillan's group reported the first catalytic enantioselectivecyclization strategy for accessing steroidal and terpenoidalframeworks using organocatalysis. In near future, more efficient and more effective catalytic biomimetic polyene cyclization reactions areexpected to be developed.
Tierische Sekrete, Drüsen und andere Organteile mit starken Geruchseigenschaften haben den Menschen seit Tausenden von Jahren in seinen Bann gezogen. Magische Kräfte — so glaubte man — sollten die ausströmenden Düfte begleiten. So wurden tierische Drogen zunächst für religiöse und kultische Zwecke verwendet. Seit dem Altertumn kennt man verschiedene Anwendungsformen: u.a. als Arzneimittel und Duftstoffe. Ambra, Moschus, Zibet und Bibergeil gehören auch heute noch zu den kostbarsten Ingredienzen der Parfümerie. Ihre Chemie setzte zögernd und erst Anfang dieses Jahrhunderts mit der Isolierung einiger flüchtiger Komponenten ein. In der Struktuaufklärung gab es Mitte der 20er Jahre erste Erfolge durch die Entdeckung macrocyclischer Moschusriechstoffe. Während der30erJahre begannen synthetische Arbeiten zu ihrer Herstellung in technischem Maßstab, die bis heute ungebrochen weitergeführt werden.
The physical and chemical properties required of a suitable sensory active molecule are determined by the location, molecular architecture and physiological medium of the chemoreceptor. Clearly sensory activity in human olfaction is exclusively associated with volatile molecules. The higher limit of molecular weight found for odorants is around 300 (for some examples, see Refs 1–3). Chemical reactivity of a ligand has little if any direct connection with olfactory activity since odorant molecules are uncharged and hardly require metabolic activation. Nevertheless, several molecular requirements must be met. Thus most odorous molecules contain both a strong hydrophobic and a relatively weak polar region. The latter, usually termed the ‘osmophore’,⁴ is associated with a functional group such as carbonyl, hydroxyl, occasionally an ether or a limited variety of heteroatomic homologues. However, the presence of a functional group is not a conditio sine qua non for receptor interaction. Even alkanes can have distinctive odours.
(±)-Ambrox (10), the racemic form of (−)-Ambrox®, the commercially most important ambergris odorant has been synthesized from a readily available bicyclic keto ester in five steps. The racemic ether retains the characteristic scent of fine-quality ambergis, and the odor threshold of the racemate and the (−)-enantiomer prepared from natural sclareol were found to be essentially identical.
We decided to follow the so-called “collective total synthesis” approach to synthesize several structurally different molecules from a common intermediate possessing appropriate stereochemistry and functionalities. As the common precursor for the efficient preparation of these bioactive molecules, we chose (+)-3,4-dihydro-γ-ionone (1), a natural compound present in minor quantities in ambergris and in the plant Bellardia trixago. Thus, we report herein the enantioselective synthesis of siccanochromene F (2), metachromins U (3) and V (4), and bicyclic squalene derivative 5 as well as the formal syntheses of ambrein (6), phenazinomycin (7), and (–)-siccanin (8).
This paper examines the cultural, scientific and poetic life of ambergris in the seventeenth century, in the context of contemporary theories about smell, and changing attitudes to style and expression. Most widely used as an ingredient in perfumery, this mysterious substance (now known to be the pathological secretion of a sperm whale) attracted significant interest: natural philosophers speculated on its origin, and imaginative writers used it as a trope for the exotic and the powerfully ephemeral. In surveying the appearance of ambergris in natural philosophical writings (including the proceedings of the Royal Society, and works by Browne and Boyle), as well as in botanical treatises, recipe books, travellers’ narratives, and lyric poetry, this paper seeks to recover a sense of the forgotten olfactory codings of the past. It ends with an attempt to place ambergris within the highly nuanced vocabulary of scent employed by Robert Herrick, the most distinguished nose of the early modern age.
Terpenes are a large class of natural products, many of which are used in cosmetics, pharmaceuticals, or biofuels. However, terpene׳s industrial application is frequently hindered by limited availability of natural sources or low yields of chemical synthesis. In this report, we developed a modular platform based on standardized and exchangeable parts to reproduce and potentially expand the diversity of terpene structures in Saccharomyces cerevisiae. By combining different module-specific parts, we exploited the substrate promiscuity of class I diterpene synthases to produce an array of labdane-type scaffolds. These were subsequently modified by a scaffold decoration module consisting of a mutant library of a promiscuous cytochrome P450 to afford a range of hydroxylated diterpenes. Further P450 protein engineering yielded dedicated and efficient catalysts for specific products. Terpenes produced include precursors of pharmacologically important compounds, molecules that are difficult to obtain from natural sources, or new natural products. The approach described here provides a platform on which additional gene mining, combinatorial biosynthesis, and protein engineering efforts can be integrated to sustainably explore the terpene chemical space.
Terpenes have numerous applications, ranging from pharmaceuticals to fragrances and biofuels. With increasing interest in producing terpenes sustainably and economically, there has been significant progress in recent years in developing methods for their production in microorganisms. In Saccharomyces cerevisiae, production of the 20-carbon diterpenes has so far proven to be significantly less efficient than production of their 15-carbon sesquiterpene counterparts. In this report, we identify the modular structure of geranylgeranyl diphosphate synthesis in yeast to be a major limitation in diterpene yields, and we engineer the yeast farnesyl diphosphate synthase Erg20p to produce geranylgeranyl diphosphate. Using a combination of protein and genetic engineering, we achieve significant improvements in the production of sclareol and several other isoprenoids, including cis-abienol, abietadiene and β-carotene. We also report the development of yeast strains carrying the engineered Erg20p, which support efficient isoprenoid production and can be used as a dedicated chassis for diterpene production or biosynthetic pathway elucidation. The design developed here can be applied to the production of any GGPP-derived isoprenoid and is compatible with other yeast terpene production platforms.
A one-pot high-yielding synthesis of silylated 2,7-dioxabicyclo[2.2.1]heptanes from oxoallylsilanes is described. The mechanism of this tandem reaction is a sequential epoxidation of the allylsilane moiety and subsequent intramolecular cyclization. This simple protocol allows the synthesis of epoxy-bridged tetrahydropyrans from allene in two high-yielding steps: silylcupration of allene (followed by capture of the intermediate cuprate with enones) and treatment of the oxoallylsilanes thus obtained with MCPBA. However, under the same conditions, oxovinylsilanes yielded epoxysilyl ketones in a very stereoselective manner.
We report the enantioselective synthesis of the ambergris odorants (+)‐(S)‐γ‐ionone, (+)‐(S)‐γ‐dihydroionone, (−)‐α‐ambrinol, (+)‐(S)‐γ‐coronal, (−)‐(S)‐γ‐homocyclogeranyl chloride and (+)‐(S)‐γ‐homocyclogeraniol. At first, the enantio‐enriched (4R,6S)‐4‐acetoxy‐γ‐ionone was prepared starting from commercial racemic ionone alpha by means of a chemo‐enzymatic process. This chiral building block was then converted into (S)‐γ‐dihydroionone which was used as the starting material for the synthesis of the aforementioned odorants. Copyright © 2012 John Wiley & Sons, Ltd.
Rules for the occurence of the ambergris odor is presented and discussed in terms of the relationship between chemical structure and odor. A general overview of the major approaches in the synthesis of Ambrox® , the key ambergris-type compound, is also presented.
Starting from inexpensive (E)-β-farnesene (1), an eight-step enantioselective synthesis of the olfactively precious Ambrox® ((−)-2a) has been performed. The crucial step is the catalytic asymmetric isomerization of (2E,6E)-N,N-diethylfarnesylamine (3) to the corresponding enamine (−)-(R,E)-4a, applying Takasago's well-known industrial methodology. The resulting dihydrofarnesal ((+)-(R)-5) (90% yield, 96% ee), obtained after in situ hydrolysis (AcOH, H2O), was then cyclized under catalytic SnCl4 conditions, via its corresponding unreported enol acetate (−)-(R)-4b, to afford trans-decalenic aldehyde (+)-6a. Subsequent transformations furnished bicyclic ketone (−)-8a and unsaturated nitrile (+)-11, both reported as intermediates to access to (−)-2a.
The synthesis of nor-ambreinolide (2) from cis-abienol (1) was carried out by direct treatment with OsO4-NaIO4 or RuO4-NaIO4. The oxymercuriation-demercuriation of 1 led to a mixture of 8,12-epoxylabdanes (5–17) which was also converted into nor-ambreinolide by treatment with RuO4-NaIO4. The formation pathways of such epoxy derivatives are discussed.
Two routes for preparing Ambrox® (1) from the methyl esters of trans-communic acid (2b) and/or cis-communic acid (3b), via selective degradation of their side chains, stereoselective formation of the tetrahydrofurane ring, and reduction of the axial methoxycarbonyl group, are described.
A mixture of the methyl esters of communic acids (3b, 4b, 5b) was used in the synthesis of the ambergris-type odorants Ambrox® (1) and ambracetal (2). Both syntheses involve methyl ketone 7 as the key intermediate.
Iododecarboxylation of labdanolic acid (1), followed by dehydrohalogenation led to alkenes 4 and 12. Both compounds were converted into (1R,2R,4aS,8aS)-1-(2-hydroxyethyl)-2,5,5,8a-tetramethyldecahydro-2-naphthalenol (8), which was transformed via cyclization into (−)-Ambrox® (9).
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The synthesis of nor‐Ambreinolide (8) from (‐)‐sclareol (1) was carried out by treatment with KMnO4‐Ac2O and further alkaline hydrolysis. 8 was directly transformed into (‐)‐ambrox (11) by reduction with metal borohydride in the presence of Lewis acids.
(-)-(4aS,8aR)-5,5-8a-trimethyl-trans-decaline 1 was prepared in a stereoespecific synthesis of 4 steps and 38% yield. The key-step involves an asymmetric Robinson annulation via Michael addition of chiral imine.
This review gives an updated account on the phenomena of enantioselective perception of chiral fragrances employed in fine and functional perfumery, and of some selected flavours. Differences between enantiomers both in odour quality and strength have been considered.“Il est des parfums frais comme des chairs d’enfants,“The perfume is as fresh as the flesh of an infant,doux comme les hautbois, verts comme les prairies,Sweet as an oboe, green as a prairie,—et d’autres, corrompus, riches et triomphants,—And the others, corrupt, rich and triumphant,ayant l’expansion des choses infiniesEnlightened by the things of infinity,comme l’ambre, le musc, le benjoin et l’encens,Like amber, musk, benzoin and incense,qui chantent les transports de l’esprit et des sens”That sing, transporting the soul and sense”(C. Baudelaire, Les Fleurs du Mal, Correspondances)(translated by William A. Sigler)
(+)-Amberketal (1) and its analog (2) have been synthesized from commercially available l-abietic acid (3) by a selective reduction of an unsaturated aldehyde in the presence of a ketone and simultaneous reduction of an iodide using an aqueous suspension of Raney Ni as the key step.
A synthesis of the valuable amber-type odorant Ambrox® from labdanolic acid (main diterpenoid of the acid fraction of non-polar extracts of Cistus ladaniferus L.) is reported. The conversion is based on (a) the α,β-dehydrogenation of methyl labdanolate using an organoselenium reagent, (b) subsequent oxidative degradations of the side chain, and (c) final acid-promoted cyclization of the resulting tetranorlabdan-8α,12-diol. The influence of the temperature and solvent in the cyclization of the diol with p-toluenesulfonic acid is also described. Thus, Ambrox® has been obtained by a six-step procedure in 33% overall yield from methyl labdanolate.
The first total synthesis of (+)-ambrein (1), a triterpene alcohol isolated from ambergris, was achieved. Both the enantiomers of ambrox® (2) were also synthesized.
Conformational factors have been found responsible for the dramatic change in odor between (−)-deoxyambreinolide (12) and its (+)-epi derivative 13. The presumably molecular event during the receptor interaction has been simulated by the diastereoisomeric 11-methyl-ambrox derivatives 3 and 5 as model compounds.
It has been shown that ambrinol is composed of at least two and probably three double-bond-isomers. In this mixture we have been able to identify the presence of α- and of γ-ambrinol, having the constitutions of 1, 1,6-trimethyl-6-hydroxy-1, 2,3,5,6,7,8,9- and -1,2,3,4, 7,8,9,10-octahydronaphthalene (III and V) respectively.
Es wird eine ergiebige Überführung des (−)-Sclareols in (+)-Manool beschrieben, die auf der selektiven Esterpyrolyse des Di-O-acetyl-(−)-sclareols beruht.
Summary One of the products of the chromic acid oxidation of the animal triterpene ambreine (V) has been identified with the lactone C16H26O2 (III) which
Die Synthese der Homofarnesylsäure und ihre säurekatalysierte Cyclisation zu drei kristallisierten carbobicyclischen (±)-Lactonen wird beschrieben.
Eighteen new sesquiterpenoid theaspirane derivatives 3–20, representing potential natural compounds, were synthesized from 1,2-didehydro-β-monocyclonerolidol (1). Their structure and configuration were determined by spectroscopic methods.
Compounds 2 to 7 were identified among the products obtained from ambrein (1) by potassium permanganate oxidation; (+)-dihydro-γ-ionone (3) was shown to have the S-configuration.
New Ambra Odorants by Photoreactions of 15, 16-Dinorlabd-8(20)-en-13-one.
UV.-irradiation of 15,16-dinorlabd-8(20)-en-13-one (1) led to the fragmentation product 4 and its photo-cyclisation product 5. Ethers 6 and 7 and the βγ-unsaturated alcohols 8 and 10 were formed via ketone 9, a double bond isomer of 1. The olfactory properties of the photo-products are described.
In the presence of HCl or BF3 dihydro-α-ionone undergoes cyclisation. In solutions in primary alcohols ROH, this cyclisation leads to bicyclic ethers V with a semicyclic double-bond. In secondary butyl alcohol the bicyclic alcohol XII is produced. Bicyclic hydro-carbones are formed as byproducts. In benzene solution BF3 forms an unsaturated bicyclic epoxyde XVII. The infrared spectra of some of these substances are discussed.
24-methyl-dihydro-γ-ionone and trans-dihydro-γ-irone have been prepared and cyclized to 1,1-dimethyl-6-ethyl-6-hydroxy-octalene (XVII) and 1,1,2,6-tetramethyl-6-hydroxy-octalene (XVIII) respectively. Whereas the first isomerization is much easier than that of dihydro-γ-ionone, the second is much more difficult.
La cyclisation de l'acide farnésyl‐acétique (VI) préparé en partant du nérolidol (III) donne une lactone C 17 H 28 O 2 , F. 136–138°, qui est le racémique de l'ambréinolide F. 141° (VII). L'identité de la structure chimique des deux lactones ressort de l'identité de leurs spectres infrarouges. Nous avons préparé plusieurs dérivés de l'ambréinolide racémique. L'oxyde C 17 H 30 O, F. 78–79° (IX), a le même spectre infrarouge et la même odeur ambrée que l'oxyde F. 82–84° préparé à partir de l'ambréine.
Zusammenfassung Die Struktur eines durch säurekatalytische Isomerisation von Ambreinolid entstehenden tricyclischen Ketons C17H26O wurde aufgeklärt.
The Conversion of Eperuic Acid into Ethers of the enantio-14, 15-Dinorlabdane Series
5 and 6 are strongly odiferous substances of the ambra-type. Their enantiomers 7 and 8, hitherto unknown, have been synthesized from eperuic acid (4) and their olfactory properties compared with those of 5 and 6. 4 was esterified by CH2N2 and dehydrogenated with (C6H5Se)2/H2O2 to the α,β-unsaturated ester 9 (61%). Oxidation by KMnO4 in acetone yielded the ketone 3 (60%). Epoxidation followed by treatment with acid converted 3 into the acetals 7 (61%) and 8 (14%). 7 and 8 differ from 5 and 6 in odor intensity, and 6 and 8 show slightly different odor quality.
Twelve tricyclic ethers of the labdane and ent ‐labdane series, 5–16 , have been synthesized; compounds 6–15 are new. The intramolecular C 18 ‐acetals 1–4 and the tricyclic ethers 5–16 were submitted to an olfactory test which was characterized by an exceptionally high percentage of ‘wrong’ answers ( cf. Table 1 , footnote b). For most compounds specific anosmia, rapidly ensuing fatigue and a high percentage of odor deviation were the most salient features.
Pronounced ambergris‐like odors were only noted in compounds of the labdane series, and were strongest in ethers 1, 5 and 15 , followed by the ethers 9 and 11 . In contrast, both labdane derivatives 3 and 7 were practically odorless. Their enantiomers 4 and 8 , on the other hand, have relatively strong odors which can only to a limited extent be associated with ambergris‐type odors. The pairs of ethers 3/4 and 7/8 are the first recorded examples of optical antipodes in which only one isomer possesses olfactory properties.
Stereochemistry-odor relationships in the 1-decalone series and their oxa-analogs.
The olfactory relationships of (−)-(9S,10S)-5,5,9-trimethyl-trans-1-decalone (2a), 6 diasterioisomers in the 11-nordriman-9-one series (2b-g), and 20 racemic 2-oxabicyclo[4.4.0]decanes are reported and correlated with the ‘Triaxial Rule of Odor Sensation’. This rule also is applied to the two internal C(13) acetals derived from (±)-dihydro-γ-ionone as well as to two epimeric C(18) ethers in the labdane series. Syntheses are described for most of the compounds examined.
Die säurekatalysierte Cyclisation von Monocyclohomofarnesylsäure-äthylester liefert drei carbobicyclische stereoisomere racemische Laktone, deren konfigurative Beziehungen zu den drei bekannten optisch aktiven raumisomeren Laktonen untersucht werden. Die Laktone mit Schmp. 79° und Schmp. 97° erweisen sich als Racemate der aktiven Isomeren mit Schmp. 93° bzw. 133°. Für das dritte inaktive Lakton wird eine Raumformel vorgeschlagen.
On a transformé le sclaréol en ambréinolide.
The degradation of manool (I) to the known intramolecular ketal III and its new stereoisomer IV is described. Structure and configuration of both stereoisomers are discussed on the basis of further chemical transformations and of the results of NMR.-spectroscopy. Both ketals possess a powerful odour of a novel amber type.
Die Darstellung des γ-Cyclo-homo-citrals (V), γ-Cyclo-homo-geraniols (VI) und γ-Cyclo-homo-geraniumsäure-methylesters (XII) durch Esterpyrolyse ihrer O-Acetyl-Derivate wird beschrieben und die Stereochemie des 2.5.5.9-Tetramethyl-hexahydro-1.4-chromens (II) und seiner Abbauprodukte festgelegt.
Beim oxydativen Abbau von Manool (I) mit Kaliumpermanganat entsteht neben dem bereits beschriebenen Methyl-keton C18H30O (II) eine neutrale Verbindung C18H30O2, welche die Konstitution eines intramolekularen Acetals IV besitzt. Die Verbindung IV weist einen starken, dauerhaften und angenehmen Ambrageruch auf, der auf die intramolekulare Acetal-Gruppierung zurückzuführen ist.
Veresterung, Hydrierung und oxydativer Abbau sowie die Bestimmung der Konfiguration an C-13 des Larixols werden beschrieben.
The biogenetic isoprene rule in its application to the triterpenes is discussed from a stereochemical standpoint. On the basis of a well defined system of arbitrary assumptions a scheme has been developed leading from squalene to the formulae of the basic representatives of all known cyclic triterpene groups - i.e. euphol, tirucallol, lupeol, taraxasterol, germanicol, β-amyrin, taraxerol, friedelin, α-amyrin, lanosterol - in their full structural and configurational detail. This result is considered to support the squalene hypothesis of the biogenesis of cyclic triterpenes.
La réduction de la lactone I, de l'hydroxyacide VI, de l'acétoxyacide VII ou de l'ozonide de l'oxyde non saturé XII par l'hydrure de lithium-aluminium donne le glycol II avec un bon rendement.
It has been shown that electrophilic reagents isomerise dihydro--ionone very easily to a bicyclic tertiary alcohol IV.
The isomerisation of bicyclohomofarnesic substances has been investigated. Several new isomers have been prepared and their infrared spectra determined and discussed.
On a préparé par dégradation du sclaréol, le bicyclohomofarnésal, le bicyclohomofarnésol, et la tétraméthyl-1,1,6,10-éthyl-5-oxido-6,52-décaline.
The fraction b.p. ≦ 84° (0.001 Torr) from Burley tobacco condensate was carefully investigated using fractional distillation and preparative column and gas liquid chromatography aided by GLC/MS coupling. Among the 193 compounds thus separated and characterized by their spectral data, 81 were newly identified tobacco constituents.
Most of the compounds isolated in the course of this work display flavouring properties which make them highly suitable for improving the flavour and aroma of tobacco and tobacco smoke.
The synthesis of racemic stereoisomeric compounds with the 5,5,9‐trimethyldecalin skeleton and an oxygen function at C(1), C(2), or C(3) is described Although racemic decalins are described, only the enantiomer related to steroids is drawn. The projection of the decalins was chosen so as to place the angular methyl group above the plane of the molecule and the oxygen function at C(1), C(2) or C(3) on the left side, as represented by formula 1–6 . The relative configuration of the substituents in decalins is designated by using the convention of the steroid series: β, meaning on the same side as the angular methyl group at C(9) and α, meaning on the side opposite from the angular methyl group. The prefix cis or trans refers to the fusion of the decalin ring system, not to the position of the substituents.
. A novel general one‐step synthesis of 2‐decalones by means of acid catalyzed cyclization of acyclic or monocyclic precursors has been developed.