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1
NATURAL RESINS: CHEMICAL CONSTITUENTS AND MEDICINAL USES.
Lorenzo Camarda, Vita Di Stefano, Rosa Pitonzo.
Department of Chemistry and Pharmaceutical Technology, University of Palermo.
Via Archirafi, 32 90123 Palermo, Italy.
Corresponding author: rosapitonzo@unipa.it
ABSTRACT
Plants and their exudates are used worldwide for the treatment of several diseases and novel
drugs continue to be developed through phytochemical research. There are more than 20,000
species of high vegetables, used in traditional medicines that are sources of potential new drugs.
Following the modern medicine and drug research advancing, chemically synthesized drugs have
replaced plants as the source of most medicinal agents in industrialized countries. However, in
developing countries, the majority of the world’s population cannot afford pharmaceutical drugs
and use their own plant based indigenous medicines. Several exudates from plants are well-known
in folk medicine since ancient time, and they are today employed also for practical uses.
Dragon’s blood is a deep red resin, which has been used as a famous traditional medicine
since ancient times by many cultures. Dragon's blood is a non-specific name for red resinous
exudations from quite different plant species endemic to various regions around the globe that
belong to the genera Dracaena (Africa) and Daemonorops (South-East Asia), more rarely also to
the genera Pterocarpus and Croton (both South America).
Dracaena draco L. is known as the dragon’s blood tree, and it’s endemic to the Canary Islands and
Morocco. Phytochemical studies of resins obtained from incisions of the trunk of D. draco, have led
to the isolation of flavans, along with homoisoflavans, homoisoflavones, chalcones and
dihydrochalcones. Dragon’s blood has been used for diverse medical applications in folk medicine
and artistic uses. It has astringent effect and has been used as a hemostatic and antidiarrhetic drug.
Frankincense, also known as Olibanum, is an old-known oleogum resin obtained from the
bark of trees belonging to the genera Boswellia. There are 43 different reported species in India,
Arabian Peninsula and North Africa. The importance of these plants is related to the use of extracts
and essential oils of resin in traditional medicine like Ayurvedic and Chinese. Extracts from B.
serrata resin are currently used in India for the treatment of rheumatic diseases and ulcerative
colitis. Furthermore, the extracts and essential oils of frankincense have been used as antiseptic
agents in mouthwash, in the treatment of cough and asthma and as a fixative in perfumes, soaps,
2
creams, lotions and detergents. In ancient Egypt the resin was used in mummification balms and
unguents. Today frankincense is one of the most commonly used resins in aromatherapy.
The biological activity of frankincense resins is due to the pentacyclic triterpenic acids, α- and β-
boswellic acids and their derivatives, which showed a well documented anti-inflammatory and
immunomodulatory activities.
Manna is an exudate from the bark of Fraxinus trees (Oleaceae). Originally it was only
collected from trees with damaged bark, but later in southern Italy and northern Sicily plantations
were established for manna production, in which the bark is intentionally damaged for exudation
and collection of manna.
In July-August a vertical series of oblique incisions are made in the bark on alternate sides of the
trunk. A glutinous liquid exudes from this cut, hardens as it oxidises in the air into a yellowish
crystalline mass with a bittersweet taste, and is then harvested. Manna is still produced in Sicily,
mainly in the Castelbuono and Pollina areas, from Fraxinus ornus and Fraxinus angustifolia trees.
The main component of manna is mannitol; it also contains glucose, fructose, maltotriose,
mannotetrose, minerals and some unknown constituents.
Manna is a mild laxative and an excellent purgative, it is suitable in cases of digestive problems, in
atonic or spastic constipation. It’s useful as expectorant, fluidifier, emollient and sedative in coughs;
as a decongestant in chronic bronchitis, laryngitis and tonsillitis; in hypertonic solutions it acts as a
dehydrating agent in the treatment of wounds and ulcers. It can be used as a sweetener in cases of
diabetes as it does not affect glycemia levels or cause glycosuria; in addition it is also a cholagogue
as it promotes the flow of the contents of the gall bladder and bile ducts and so stimulates bile
production.
3
INTRODUCTION
Many higher plants produce economically important organic compounds such as oils, resins,
tannins, natural rubbers, waxes, dyes, flavors and fragrances, pharmaceuticals. However, most
species of higher plants have never been described, much less surveyed for chemical or biologically
active constituents, and new sources of commercially valuable materials remain to be discovered.
Extractable organic substances accumulate in quantities sufficient in many plants, are economically
useful as chemical feedstocks or raw materials for various scientific, technological, and commercial
applications. For the sake of convenience, plant chemicals are often classified as either primary or
secondary metabolites.
Primary metabolites are substances widely distributed in plant kingdom and are often concentrated
in seeds and vegetative organs. These compounds are needed for physiological development
because of their role in basic cell metabolism, and they are also used as industrial raw materials,
foods, or food additives.
Secondary metabolites are compounds biosynthetically derived from primary metabolites but more
limited in distribution in the plant kingdom, being restricted to a particular taxonomic group
(species, genus, family, or closely related group of families). These compounds, accumulated by
plants in smaller quantities than primary metabolites, have no apparent function in a plant's primary
metabolism but often have an ecological role. The resins, secretions of many plants, are used
widespread as adhesives, ingredients of cosmetic preparations, as fragrances in daily rituals and
religious ceremonies, as coating materials and as remedies in folk medicine [1].
In the first Pharmacopoeia written by the Greek botanist Dioscorides [2] there were around 600
advised remedies, which were prepared from mixtures of natural resins and balsams as well as some
herbal preparations. The antiseptic activity of resins was assumed to be known long before as both
the Egyptians used to burn a special mixture of them during plague and the Indians used gurjun
balsam against leprosy.
It is known that Hindus, Babylonians, Assyrians, Persians, Romans, Chinese and Greeks as well as
the people of old American civilisations like Incas, Mayas and Aztecs, used natural resins primarily
for embalming. For the same purpose, Egyptians used styrax (Liquidamber orientalis), myrrh
(Commiphora spp.), colophonium (Pinus palustris), cedar (Cedrus spp.) and labdanum (Cistus
ladaniferus). During sacrification ceremonies resins were burned to prevent the influence of bad
spirits on souls and Egyptians used olibanum (Boswellia spp.), myrrh, bdellium (Commiphora
wightii), mastic (Pistacia lentiscus), styrax, santal (Santalum album), cinnamon (Cinnamomum
aromaticum), aloe wood (Aloe succotrina), cedar and juniper (Juniperus communis).
4
Dragon’s blood is a non-specific name refers to reddish resinous products, usually occur as
granules, powder, lumps or sticks, which has been used as a famous traditional medicine since
ancient times. The origin of the resin is believed to be from Indian Ocean island of Socotra, now
part of Yemen [3] and several alternative sources are from Canary Islands, Madeira, and South East
Asia and also from East and West Africa have been identified [4]. However, there is a great degree
of confusion regarding the source and identity of this resin.
This particular name is applied to many red resins described in the medical literature, e.g. East
Indian Dragon’s blood (from the fruit of Daemonorops draco (Willd.) Blume), Socotran or
Zanzibar Dragon’s blood (exudates of Dracaena cinnabari Balf. f.), Canary Dragon’s blood
(exudates from the trunk of Dracaena draco (L.) L.), West Indian Dragon’s blood (exudates of
Pterocarpus draco L.), Mexican Dragon’s blood (resin of Croton lechleri Müll. Arg.) and the
Venezuelan Dragon’s blood (resin of Croton gossypifolium Vahl) [5]. Thus, the name Dragon’s
blood in general is used for all kinds of resins and saps obtained from four distinct plant genera
Croton (Euphorbiaceae), Dracaena (Liliaceae), Daemonorops (Palmaceae), and Pterocarpus
(Fabaceae) [6].
Dracaena draco L. is known as the dragon’s blood tree. D. draco subsp. draco was found in
the Madeira, Canary and Cape Verde archipelagoes, and subsp. ajgal in Morocco. The resin exudes
from the wounded trunk or branches of the tree (Figure 1).
Figure 1: Dragon’s blood resin from Dracaena draco.
5
According to a Greek myth, Landon, the hundred-headed dragon, guardian of the Garden of the
Hesperides (the nymph daughters of Atlas, the titan who holds up earth and heaven) was killed by
either Hercules (in his quest) or Atlas (as punishment) while bringing back three golden apples from
the garden, depending upon the version of the myth. Landon’s red blood flowed out upon the land
and from it sprung up the trees known as Dragon Trees [7]. Dragon’s blood was also called Indian
cinnabar by Greek writers. The name Dragon’s blood dates back to the 1st century B.C. when a
Greek sailor wrote, in a shipping manual “Periplus of the Erythrean Sea”, about an island called
Dioscorida where the trees yielded drops of cinnabar. Plinius [8] also described that the resin got its
name from an Indian legend based on Brahma and Shiva. Emboden [9] and Lyons [10] had also
summarized the history and mythology of Dragon’s blood. According to Lyons, the struggle
between a dragon and an elephant that, at its climax, led to the mixing of the blood of the two
creatures resulted in a magical substance, Dragon’s blood imbued with medicinal properties.
Dragon’s blood has been used for several applications, including artistic uses and folk medicine.
The resin from Dracaena was used for ceremonies in India, as red varnish for wooden furniture in
China, to color the surface of writing paper for banners and posters, especially for weddings and for
Chinese New Year, as pigment in paint, enhancing the color of precious stones and staining glass,
marble and the wood for Italian violins. Dragon's blood from Dracaena draco was detected in a
broad variety of art objects dating from the fifteenth to the nineteenth centuries [11]. It was
predominantly used in gold lacquers and Hinterglasmalerei (reverse-glass paintings), and relatively
rarely in glazes on conventional paintings or lacquers on furniture. In all these cases, the artists took
advantage of the special properties of dragon's blood because of a film-forming resin with a natural
red colour that is nevertheless translucent. In lacquers, dragon's blood was mixed with other natural
resins such as sandarac [12], larch turpentine [13] and mastic [14], and also with other red resins
such as shellac or gum benzoin, which is a dark red balsamic resin obtained from several species of
the genus Styrax [15].
Dragon’s blood was used by early Greeks, Romans, and Arabs for its medicinal properties. Locals
of Moomy city on Socotra island used the resin from Dracaena draco as a sort of cure-all, by using
for general wound healing, coagulant, curing diarrhoea, lowering fevers, dysentery diseases,
internal ulcers of mouth, throat, intestine and stomach, respiratory and stomach viruses and skin
disorders such as eczema. Dioscorides and other early Greek writers described its medicinal uses.
Dragon’s blood resin has strong astringent properties and is used as a muscle relaxant [16]. It was
also used to treat gonorrhea, stoppage of urine, watery eyes and minor burns [17].
6
Compounds in dragon’s blood resins that could be associated with the red colour, were
studied by Brockmann and Junge [18], who attributed the color to the group of compounds known
as anthocyanins. Dracoflavylium (7,4'-dihydroxy-5-methoxyflavylium) was isolated and
characterized from a commercial source of powdered dragon’s blood resin that was obtained from a
species D. draco [19]. The red colour of dragon’s blood resin is associated with the red quinoid
bases of the respective yellow flavylium cations [19].
OHO
OH
OCH
3
OO
OH
OCH
3
+ H
+
In solution, both forms are connected, and can undergo multiple structural transformations, in what
can be described as a multistate system, reversibly interconverted by external stimuli, such as pH
[19–24]. Since compounds with a flavylium chromophore have not been found in the red resins or
exudates from the species of Croton and Pterocarpus called as dragon’s blood [25], it suggests that
this chromophore can be used as marker to identify resins origin obtained from D. draco [26].
Phytochemical studies carried out on D. draco resins, have led to the isolation of the most abundant
resin constituents, belonging to the class of flavonoids: flavans (1-5), along with homoisoflavans (6-
7) and homoisoflavanones (8-15). In addition were isolated chalcones and dihydrochalcones [27-
30].
7
O
R
R
1
R
3
R
4
R
2
(1) R =CH
3
, R
1
=OH, R
2
=H, R
3
=OCH
3
, R
4
=OH;
(2) R =CH
3
, R
1
=OH, R
2
=H, R
3
=OH, R
4
=OCH
3
;
(3)
R =H, R
1
=OH, R
2
=H, R
3
=OH, R
4
=OCH
3
;
(4) R =CH
3
, R
1
=OH, R
2
=H, R
3
=OH, R
4
=H;
(5) R =CH
3
, R
1
=OCH
3
, R
2
=OH, R
3
=OH, R
4
=H
O
X
R
2
R
OHR
1
R
3
(6)
R =H, R
1
=OH, R
2
=H, R
3
=H, X =H
2
(7) R =H, R
1
=OH, R
2
=H, R
3
=OCH
3
, X =H
2
(8) R =H, R
1
=OH, R
2
=H, R
3
=H, X =O
(9) R =OH, R
1
=H, R
2
=OH, R
3
=H, X =O
(10)
R =H, R
1
=OH, R
2
=H, R
3
=OH, X =O
(11)
R =OH, R
1
=OCH
3
, R
2
=OH, R
3
=H, X =O
(12) R =OH, R
1
=OH, R
2
=OCH
3
, R
3
=H, X =O
(13) R =H, R
1
=OH, R
2
=CH
3
, R
3
=OH, X =O
(14) R =OH, R
1
=CH
3
, R
2
=OH, R
3
=H, X =O
(15)
R =CH
3
, R
1
=OH, R
2
=CH
3
, R
3
=OH, X =O
Regarding the biological activity of the resin obtained from D. draco, no data is reported in the
literature. Preliminary experimental data not yet published, concern the in vitro antibacterial and
anti-biofilm activities of acetonic extracts obtained from Dracaena draco resin, collected from a
specimen tree which grows in the Botanical Garden of the University of Palermo.
8
The antimicrobial and anti-biofilm activities of acetone extracts were evaluated against different
Gram-positive and Gram-negative bacteria strains. In particular was found a considerable
antibacterial activity against Staphylococcus aureus and Staphylococcus epidermidis, with MIC
values of 100 µg/mL, and an interesting anti-biofilm activity against preformed S. aureus biofilms,
with MIC values ranging from 54 and 39% at concentrations between 200 and 50 µg/mL.
The efficacy of these acetonic extracts should be considered as an important factor in evaluating
them as an interesting source of innovative plant derived antimicrobial agents that can be used in
the development of new strategies to treat biofilms of medical relevance.
Flavonoids are one of the largest groups of secondary metabolites, and they play an important role
in plants as defence and signalling compounds in reproduction, pathogenesis and symbiosis [6,31].
Plant flavonoids are involved in response mechanisms against stress, as caused by elevated UV-B
radiations [32-35], infection by microorganisms [36] or herbivore attack [37]. They are pigment
sources for flower colouring compounds [38] and play an important role in interactions with insects
[39]. They also affect human and animal health because of their role in the diet, which is ascribed to
their antioxidant properties [40] or their estrogenic action [41], and to a wide range of antimicrobial
and pharmacological activities [42,43].
Some of the flavonoid compounds isolated and identified in Dracaena draco resin were also
identified in its fruits samples collected from a specimen tree which grows in the Botanical Garden
of the University of Palermo. In particular, were performed MS-MS experiments that afforded to
identify some homoisoflavanone compounds (8-15) [44]. In addition, following minor constituents
were isolated from roots, bark and aerial parts: steroidal saponins, along with known compounds
including sterols, carotenes and aromatic compounds. [45-47].
Steroidal saponins are reported to show potent cytostatic activity against HL-60 cells with IC
50
value being 1.3 and 2.6µg/mL, respectively compared with etoposide (IC
50
0.3µg/mL) used as a
positive control [45-46,48-49]. The mechanism of these compounds’ cytotoxicity was also
evaluated and found to be via activation of apoptotic process.
9
Olibanum also called Frankincense is an aromatic oleogum resin obtained from the bark of
trees belonging to the genera Boswellia of the Burseraceae family, that includes approximately 43
different species of small trees, that grow mainly in India, Arabian Peninsula and North Africa.
Some of the well-known species are: B. papyrifera (Del.) Hochst (Ethiopia and Sudan), B. neglecta
S. Moore (Kenya), B. rivae Engl. (Ethiopia), B. frereana Birdw. (Somalia), B. carteri Birdw.
(Ethiopia and Eritrea), B. orodata Hutch. and B. dalzielli Hutch. (Nigeria), B. sacra Flueck.
(Oman), B. serrata Roxb. (India) and B. thurifera Colebr. (Arabia e Somalia) [50].
Olibanum is produced in a restricted geographical area from uncultivated trees, and usually
collected by small nomadic groups; the name is derived from the Arab word “al Luban”, which
means milk and is a reference to the milky sap that exudes from the tree upon incision (Figure 2).
Appreciated by ancient civilizations, Boswellia resins ranked along with gold and ivory, spices and
textiles as valuables for trading and barter.
Figure 2: Frankincense oleogum resin sample.
Harvesting Frankincense is a time consuming process that begins in December, reaching a peak
from March to May [51]. The trees start producing resin when they are about 8 to 10 years old. [52]
A deep incision is made into the bark (according to recent research more than 5 incisions causes
considerable stress to the trees) and this wounding causes the tree to bleed a milky white substance
10
that seals and heals the wound and prevents infection; after three months the resin has hardened
enough to be scraped off the trunk.
The first mention about use of Boswellia resin as a drug is reported in the Ebers papyrus, (1500
B.C.) [51], that is the oldest list of prescriptions describing the value of resin in funerals,
mummification and cremation procedures. Early Egyptian myth describes frankincense as
representing the Horus’s tears. Later texts of Greek and Roman origin describe the trade of these
appreciated resins, which were exported to Rome, China and North Africa [52].
Between 35 and 25 B.C. Celsus recommended that frankincense be used to treat wounds, as a
possible antidote to hemlock and to stop internal bleeding and superficial bruising if mixed with
leek juice [52]. In the Babilonian Talmud (3rd–6th centuries B.C.) is reported that resin was
administered in wine to prisoners condemned to death to benumb the senses [53]. Based on this
text, some scholars assumed that the drink given to Jesus before crucifixion contained Boswellia
resin [54]. In a syriac book of medicine (5th century) frankincense is indicated as useful in the
catarrh, gout, colic treatments and gastrointestinal hemorrhage while in the work of Ibn Sina
(Avicenna) of the 11th century is reported frankincense use in inflammation and infection of the
urinary tract [52]. In the 17th century Culpepper, a herbalist practicing in the East End of London,
used frankincense to treat stomach ulcers and as a topical unguent for bruising [55]. During this
period distillates of the resin called “oils of olibanum”, were widely employed by the barber
surgeons, apothecaries and alchemists, for their appealing scent [56]. In Ethiopia resin was believed
to have a tranquilizing effect [57] and in Kenya it was used for dressing wounds and, mixed with
sesame oil, to reduce the loss of blood in the urine from schistosomiasis infestation. In India, the
applications regarded dental and skin diseases, respiratory complaints and digestive troubles. In
China resin was a constituent of several skin remedies, including those for bruises and infected
sores [52].
In Arabian countries where frankincense traditional medical use is widespread, every part of the
tree including root, bark, bud, flower and fruit, is still used. The powdered bark is made up into an
astringent paste which is used as a soothing ointment and as a remedy for swelling; it is applied as
remedy for wounds and burns, after mixing with water. The resin is chewed to treat dental
infections . Buds and fruits provide a cleansing tonic for the digestive system. The resin is used as a
decoction with Cinnamon and Cardamom to treat stomach aches.
Olibanum burnt it was also thought to act as an expectorant and in cases of colds, flu and diseases
of the upper respiratory tract. The smoke is also a powerful insect deterrent and thus served as a
prophylactic to prevent the bites of malaria carrying mosquitoes.
11
Today frankincense is widely employed in Catholic Christian ceremonies as well as other religious
and secular traditions. It is also an important component in cosmetic industry [52] and it is widely
marketed as a food supplement [58].
Phytochemical studies carried out on several Boswellia spp. resins led to the isolation of at
least 200 constituents; the chemical composition of the resins varies depending on the species [59-
60]. In general the rubbery fraction represents about one third of the natural product and it is
composed of polysaccharides, the oil fraction ranges from 5% to 10%, and the non volatile
terpenoic fraction represents about 40% including tetracyclic triterpenes with dammarane or
tirucallane skeletons, and pentacyclic triterpenoids belonging to the oleanane, ursane and lupane
classes [61]. Specific chemical markers of Boswellia resins are pentacyclic triterpenoic acids called
as boswellic acids (BAs) and their derivates, and tirucallic acids (TAs) and their derivates.
CH
3
CH
3
CH
3
CH
3
HO
CH
3
HOOC
CH
3
H
3
C
CH
3
CH
3
CH
3
CH
3
HO
HOOC CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
HOOC
H
3
C CH
3
-Boswellic acid -Boswellic acid Tirucallic acid
Research results on the structure-activity relationship between anti-inflammatory activity and
natural triterpenoids, indicated that an acid functional group increased the effect [62].
Boswellic acids (BAs) and their derivatives including acetyl-ß-boswellic acid (ABA), 11-keto-ß-
boswellic acid (KBA) and acetyl-11-keto-ß-boswellic acid (AKBA), as tirucallic acids (TAs), show
a well-documented anti-inflammatory activity [47-49]. The mechanism of action of the pentacyclic
triterpene acids, indicate that the primary site of action of these compounds is inhibition of 5-
lipoxygenase enzyme (5-LO) preventing the formation of leukotrienes (LTB
4
, LTC
4
, LTD
4
), both
acute and chronic inflammation, so they did not affect the cyclooxygenase activities and therefore
synthesis of prostaglandins [59, 66]. Studies about structure-activity relationships reported that the
pentacyclic triterpene ring system is crucial to bind the inhibitor to the highly selective effector site.
12
It has been found that compounds with 11-keto function on the skeleton, provides the best
inhibitory action on 5-LO.
Moreover, the acetoxy-derivatives potently inhibited the activities of human recombinant Akt1 and
Akt2, thus, tirucallic acid derivatives represent a new compound class with antitumor properties
[67]. Other molecular targets of BAs include human leukocyte elastase, CYP 2C8/2C9/3A4,
topoisomerase I, topoisomerase IIa, and IKK α/β that explain anti-cancer activity. For example
BAs, like activity of polyphenols, may have a role in inhibition of the human leukocyte elastase
interfering with NF
B pathway [68]; although the anti-asthmatic reports on BAs revealed that
leukotriene and elastase enzyme inhibition might be responsible for this effect [69-71].
Several clinical trials revealed a comparable efficacy of Boswellia serrata with synthetic drugs like
sulfasalazine and mesalazine in the local treatment of active Crohn’s disease and colitis ulcerosa,
with a risk-benefit analysis in favour of BAs [59,72-73]. As for their effect as an anticomplement
system, a mixture of BAs was found to inhibit the activity of C3 convertase in the classic
complement pathway, which consequently suppressed the conversion of C3 into C3a and C3b [73].
Besides their renowned anti-inflammatory activity, boswellic acids have been extensively
investigated with respect to their activity against tumor cells and chemopreventive effects.
Literature data demonstrate that BAs induce cycle arrest [73-74] and downregulate several
antiapoptotic genes [76-79].
In literature there are few studies about chemical composition and biological activity of
Boswellia resin essential oils; their composition from different Boswellia spp. depends to the
climate, harvest conditions and geographical sources of resins. Frankincense oils are prepared by
steam distillation directly from resins and have been used as topical antiseptics, antimicrobial,
healing and sedative properties and to alleviate the pain caused by rheumatism [80-82]; moreover
they are commonly used in aromatherapy practices.
Boswellia spp. resin essential oils were characterized by a combination of GC and GC/MS analyses,
that led to the identification of the chemotaxonomy marker components for each species. The main
classes of compounds identified were monoterpene hydrocarbons (HM), oxygen monoterpenes
(OM), sesquiterpene hydrocarbons (SH), oxygen sesquiterpenes (OS), diterpene hydrocarbons
(DH), oxygen diterpenes (OD), ether derivates, alcohol and ester derivates.
The GC-MS profile of B. serrata resin oil is quite similar to that of B. carteri, except for the
presence of α-thujene and methylchavicol, which should be considered as chemotaxonomy marker
components. The main components identified in B. carteri oil were: α-pinene, myrcene, limonene
13
and α-cedrene. In B. papyrifera oil, n-octyl acetate was the main constituent and n-octanol,
incensole and incensole acetate were minor components. The oleogum resin oil of B. rivae contains
hydrocarbon and oxygenated monoterpenes mainly. In accordance with the literature limonene, 3-
carene, α-pinene and trans-verbenol were the most abundant constituents, that should be considered
as chemotaxonomy markers. Thus, it was observed in this oil the complete absence of the
sesquiterpene and diterpene components [83,84]. On the other hand B. frereana oil is rich in the
monoterepens as -thujene, p-cymene and -pinene, as well B. neglecta oil. In addiction B.
frereana oil is poor in sesquiterpenes and totally devoid of the diterpenes of the incensole type [84].
Several studies reported in literature encourage the medical use of these oils as antimicrobial agents,
their antibacterial activity was evaluated by determining MIC values against several fungi, Gram-
positive and Gram-negative bacterial strains. The B. carteri resin oil demonstrated the highest
degree of activity against the methicillin-resistant S. aureus and against Pseudomonas aeruginosa,
while B. rivae resin oil showed the lowest MIC value against E. coli. Interestingly, although B.
serrata resins are the most widely studied for their high content of boswellic acids, its essential oil
was the least active against all of the tested bacterial strains [85-86].
B. rivae resin oil demonstrated a lower MIC value against Candida albicans, while B. carteri and B.
papyrifera resin oils showed good MIC values against C. albicans and Candida tropicalis. A
monoterpene hydrocarbon most notably presents in B. carteri and B. rivae oleogum resin oils was
limonene. It is known that limonene inhibits the growth of several fungal and Gram positive
bacterial strains [87].
The essential oils of Boswellia spp. have been also tested as anti-biofilm agents; in particular that of
B. papyrifera showed considerable activity against both S. epidermidis and S. aureus biofilms.
Boswellia rivae essential oil was very active against preformed C. albicans biofilms and inhibited
the formation of C. albicans biofilms at a sub-MIC concentration. The efficacy of these oils is
considered important against staphylococcal and C. albicans biofilms, that are pathogens in a
protective physiological form intrinsically resistant to conventional antibiotics [88].
14
Manna is an exudate obtained from the bark of trees belonging to the genera Fraxinus L.,
distributed mostly in the temperate regions and the subtropics of the Northern hemisphere [89-90].
The classifications of Knoblauch, Taylor and Johnson place the Fraxinus species into the tribe
Fraxineae of the subfamily Oleoideae of the Oleaceae family [89]. Knoblauch [91] describes 39
Fraxinus spp. divided in two sections: Ornus and Fraxinaster; Lingelsheim [92] recognizes 63 spp.
grouped in the same two sections. In a recent classification of Oleaceae, the subfamily level is
omitted, the family is splitted into five tribes and the genus Fraxinus consists of about 50 spp.,
including Fraxinus ornus and Fraxinus angustifolia.
Fraxinus genus are botanically described as trees or rarely shrubs, deciduous or rarely evergreen.
Leaves are odd-pinnate, opposite or rarely whorled at branch apices; inflorescences are terminal or
axillary toward end of branches; flowers are small, unisexual, bisexual, or polygamous. The corolla
is white to yellowish, four-lobed, divided to base. The fruit is a samara with elongated wing [90].
The Fraxinus species have economical, commercial and medicinal importance [89,90,93]; the
plants from this genus are widely used for timber [94].
Originally manna was only collected from trees with naturally damaged bark, but today in
Sicily plantations the bark is expressly damaged for exudation and collection of manna.
The earliest reports on the production of manna in Sicily date from the second half of 1500, but
cultivation on the island has been developed intensively only in the XVIII century. The areas of
greatest production were Castelbuono, Cefalù, Geraci Siculo, Pollina and San Mauro Castelverde,
located in Madonie National Park. Manna production from Fraxinus ornus and Fraxinus
angustifolia trees, today is mainly restrict to the Castelbuono and Pollina areas.
The collection of manna is made during the summer; a vertical series of oblique incisions known
locally as “ntacche” are made in the bark on alternate sides of the trunk, and in the main branches.
In order not to damage the plant and to preserve the abundance of the harvest, incisions should be
done by experienced hands can accurately use the appropriate tool known locally as “mannaluoru o
cutièddu â manna”, a kind of hatchet and pointed sharp.
From incisions in the trunk exude a glutinous liquid that hardens quickly to form a yellowish
crystalline mass with a bittersweet taste named manna (Figure 3).
15
Figure 3: Manna obtained from the bark of Fraxinus L. tree.
Three different types of manna are produced from Fraxinus ornus and Fraxinus angustifolia trees,
the so called manna in cannolo, manna in sorte and manna in rottame.
Manna in cannolo is the most valuable type and can be consumed as it is; it is obtained when
whitish liquid dripping form a stalactite of various lengths. Recently, to facilitate the formation of
manna in cannolo, under the incision line is placed a small metal conduit whose end is fixed nylon
held in tension by a small weight, in order to conveyed the exudate inside the metal conduit and
drips down the wire on which hardens before to fall to the ground.
Manna in sorte occurs when the production is particularly abundant and climatic conditions are
likely to slow down the solidification of the liquid along the trunk; so, the liquid drains to the
ground where it is collected in the shovels of prickly pear where hardens slowly.
Manna in rottame is exudate that hardens on the tree trunk and is the less valuable type.
16
The manna harvest is done during hottest hours of the day to facilitate the detachment of the manna
from bark and to prevent loss of liquid in the process of condensation.
Manna in cannolo is collected first and carefully placed in special wooden shelves. The residues
that remained stuck to the trunk (manna in rottame) are scraped by a metal shovel. The harvested
manna is dried in a well ventilated place, shaded the first day and on the sun in the days following.
During drying, the product is stirred properly and protected from rain and damp night in order to
avoid browning and molds proliferation.
Furthermore, the different types of manna, pending the sale, should be stored separately in sealed
wooden boxes or other containers suitable for the purpose, in dry and dark.
The Italian law December 24, 1928 No 3144, states that the name manna is assigned only to the
product resulting from incision of the cortex of “Orniello or Amolleo” (Fraxinus ornus) and of
“Ossifillo” (Fraxinus angustifolia). It is forbidden to prepare, sell, to be sold or put on the market
manna still containing sucrose, starchy substances or foreign substances of any kind, except the
natural impurities in the normal proportion for different types of manna. This law on supervision of
agricultural products to protect the authenticity of the product, provides consumers and defines the
duties of producer [95].
The main component of manna is D-mannitol, an hexavalent alcohol colorless, odorless and sweet
taste also known as “manna sugar”; it also contains other sugars such as glucose, fructose,
mannotriose, mannotetrose, minerals, water and minor constituents [96].
Manna and mannitol have pharmacological activity and are both listed in the Italian F.U. VIII Ed.
In other pharmacopoeias (IX-XII) is given only the mannitol, whereas in the European
Pharmacopoeia and the Pharmacopoeia of the United States is reported as such manna.
Manna is a mild laxative and an excellent purgative, it is suitable in cases of digestive problems, in
atonic or spastic constipation. It’s useful as expectorant, fluidifier, emollient and sedative in coughs;
as a decongestant in chronic bronchitis, laryngitis and tonsillitis; in hypertonic solutions it acts as a
dehydrating agent in the treatment of wounds and ulcers. It can be used as a sweetener in cases of
diabete as it does not affect glycemia levels or cause glycosuria; in addition it is also a cholagogue
as it promotes the flow of the contents of the gall bladder and bile ducts and so stimulates bile
production [97].
In order to increase knowledge on the biodiversity of endemic Fraxinus spp. in Sicily, were carried
out phytochemical studies on manna samples produced by trees belonging to different Fraxinus
angustifolia subsp. angustifolia and F. ornus cultivars growing in the areas of main production,
located in Madonie National Park.
17
In particular, were analyzed following cultivars locally named Verdello, Nziriddu, Baciciu, Russu,
Macigna and Sarvaggiu, all belonging to Fraxinus angustifolia subsp. angustifolia, and the cultivar
locally named Serracasale belonging to Fraxinus ornus.
Analytical investigations carried out have allowed to define the sugars composition (such as
mannitol, monosaccharides and oligosaccharides) of dried samples of manna in cannolo produced
by different cultivars, the chemical composition of the volatile fraction of several samples of fresh
manna, and the identification of some minor constituents of coumarins type.
The analysis of the sugars composition in samples of manna were performed by GC-MS
using methods described in the literature [98-100]. The abundance of sugars varies depending on
the cultivar analyzed. Were analyzed samples of manna in cannolo collected in august 2005 in the
area of Castelbuono, during the period of higher production.
Figure 4 shows a comparison between the cultivars of Fraxinus angustifolia and F. ornus, with
regard to the contents in monosaccharides (sum of glucose and fructose), oligosaccharides (sum of
mannotriose and mannotetrose) and mannitol.
0
20
40
60
80
100
NZIRIDDU
BACICIU
VERDELLO
RUSSU
MACIGNA
SARVAGGIU
SERRACASALE
monosaccharides (sum of glucose and fructose)
oligosaccharides (sum of mannotriose and mannotetrose)
mannitol
Figure 4: comparison between the cultivars of Fraxinus angustifolia and F. ornus, with regard to
the contents in monosaccharides , oligosaccharides and mannitol.
18
It could be observed that the monosaccharides content is almost constant in all cultivars, with only a
slight percentage increases for cultivars Russu (F. angustifolia) and Serracasale (F. ornus).
Regarding the content of oligosaccharides, the percentage increases significantly in the cultivars
Sarvaggiu (F. angustifolia) and Serracasale (F. ornus). Mannitol, the main constituent of sugars,
has a nearly constant percentage abundance in all cultivars analyzed [97].
The analysis of the chemical composition of the volatile fraction were performed by GC-
MS. Manna fresh samples produced by trees belonging to Nziriddu, Verdello and Baciciu cultivars,
were collected during the summer of 2004 and immediately analyzed using the SPME (Solid Phase
Microextracion). Identification of the individual components was based on matching with NIST
2005 mass spectra library database and comparison with spectra of authentic samples and literature
data. The most abundant compounds identified are esters including methyl palmitoleate, ethyl
palmitate and ethyl oleate, and alcohols such as farnesol [97]. Because of the volatility of these
compounds, their abundance percentage decreases over the residence time of the manna on the
trunk of the trees. It is therefore essential for the SPME analysis to use freshly harvested samples of
manna.
It is reported in the literature that the presence of coumarins, secoiridoids, and phenylethanoids is a
characteristic feature of Fraxinus species. These chemical constituents were isolated from bark,
leaves and flowers of Fraxinus angustifolia and ornus trees. The secoiridoids occur mainly in the
form of glucosides and esters of hydroxyphenylethyl alcohols. Lignans, flavonoids and simple
phenolic compounds are also common, but they appear to have more limited distribution. The
occurrence of coumarins distinguishes the genus Fraxinus from the other genera in Oleaceae.
Traditionally, the genus has always been associated with investigations on coumarins [94].
Even the analytical investigations carried out on samples of manna have shown the presence of
coumarin constituents. In particular, from a sample of manna in rottame were isolated compounds 1
and 2, whose structure are shown below [101].
O O
O
OH
OH
OCH
3
H
3
CO
O O
H
3
CO
OCOCH
3
O
OCOCH
3
1 2
19
Preliminary experimental data not yet published carried out by HPLC-DAD-ESI-MS, have led to
the identification of three coumarins [30]. Figure 5 shows the reconstructed chromatogram on the
basis of the total ion current (TIC) of compounds 1-3 recorded at a wavelength of 320 nm.
min
0 5 10 15 20 25 30
mAU
0
50
100
150
200
250
300
350
400
1
2
3
Figure 5: reconstructed chromatogram based on the total ion current (TIC) of compounds 1-3 recorded
at a wavelength of 320 nm.
In order to indicate a structure for the three compounds, were performed MS-MS experiments.
Through these analysis it was possible to identify the compounds as fraxidin, isofraxidin and
fraxinol, whose structures are shown below.
O O
OH
H
3
CO
H
3
CO
O O
OCH
3
HO
H
3
CO
O OH
3
CO
HO
OCH
3
Fraxidin Isofraxidin Fraxinol
20
CONCLUSIONS
Although resins discussed in this chapter have proved to be popular alternative or complementary
medicine used in the treatment of many diseases, clinical trial evaluation of these claims using
currently accepted protocols is needed. The reported resins offer huge potential as a possible
pharmacological application but it’s necessary a further investigation to verify whether purified
compounds isolated may have better therapeutic potential as compared to crude extracts.
Since there is considerable variation in the chemical composition among resins referred, quality
control/assurance needs to be established for the traditional medical trade.
Advances in chromatographic and spectroscopic techniques only now allow us isolation and
structural analysis of potent biologically active plant constituents that are present in too low
quantity to have been previously characterized. The aim of this work is an effort to highlight the
potential and problems related to the sources and possibilities of isolating new pharmaceutically
active molecules, using traditional knowledge in our search, for new and effective drugs molecules.
These new chemicals will serve to enhance the continued usefulness of higher plants and their
products as renewable resources of chemicals.
21
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