Gopalakrishnan Geetha

Gopalakrishnan Geetha
Universidad Politécnica de Cartagena | UPCT · Mining, Geological and Cartographic Engineering

PhD

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49
Publications
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Publications

Publications (49)
Article
In mosquito control programs, botanical origin may have the potential to be used successfully as larvicides. The larvicidal activity of crude acetone, hexane, ethyl acetate, methanol, and petroleum ether extracts of the leaf of Centella asiatica Linn., Datura metal Linn., Mukia scabrella Arn., Toddalia asiatica (Linn.) Lam, extracts of whole plant...
Article
The larvicidal activity of a petroleum ether extract of Zingiber officinale Roscoe (Zingiberaceae) was evaluated against Aedes aegypti L. and Culex quinquefasciatus Say (Diptera). Bioassay-guided fractionation led to the isolation of 4-gingerol (1), (6)-dehydrogingerdione (2) and (6)-dihydrogingerdione (3); the latter has not previously been report...
Article
Full-text available
The larvicidal activity of crude hexane, ethyl acetate, petroleum ether, acetone, and methanol extracts of the leaf and bark of Ficus racemosa (Moraceae) was assayed for their toxicity against the early fourth-instar larvae of Culex quinquefasciatus (Diptera: Culicidae). The larval mortality was observed after 24-h exposure. All extracts showed mod...
Article
Larvicidal activity of crude hexane, ethyl acetate, petroleum ether, acetone and methanol extracts of five medicinal plants, Abutilon indicum, Aegle marmelos, Euphorbia thymifolia, Jatropha gossypifolia and Solanum torvum were assayed for their toxicity against the early fourth-instar larvae of Culex quinquefasciatus. The larval mortality was obser...
Article
Larvicidal activity of ethyl acetate, butanol, and petroleum ether extracts of five species of Euphorbiaceae plants, Jatropha curcas, Pedilanthus tithymaloides, Phyllanthus amarus, Euphorbia hirta, and Euphorbia tirucalli, were tested against the early fourth instar larvae of Aedes aegypti L. and Culex quinquefasciatus (Say). The larval mortality w...
Article
The title compound [systematic name: (5[alpha],7[alpha],13[alpha],17[alpha])-7-(acetyloxy)-21,23-epoxy-4,4,8-trimethyl-24-norchola-1,14,20,22-tetraen-3-one], C28H36O4, was isolated from uncrushed green leaves of Azadirachta indica A. Juss (neem) and has been reported to possess antifeedant activity against Spodoptera litura similar to nimonol extra...
Article
Nimbolide [systematic name: (4alpha,5alpha,6alpha,7alpha,15beta,17alpha)-7,15:21,23-diepoxy-6-hydroxy-4,8-dimethyl-1-oxo-18,24-dinor-11,12-secochola-2,13,20,22-tetraene-4,11-dicarboxylic acid gamma-lactone methyl ester], C27H30O7, was isolated from the leaves of Azadirachta indica, and its isomer, isonimbolide [systematic name: (4alpha,5alpha,6alph...
Article
The title compounds (I) and (II) crystallize in the monoclinic space group P21/c and orthorhombic space group Pbca respectively. The inter-planar angle between the two phenyl rings are 55° in I and 24.5(1)° in II. The molecular packing of the compounds I and II are stabilized by C-H…O and C-H…π, and N-H…O, C-H…O and C-H…π interactions, respectively...
Article
Samaderin B, or (1R,2S,5R,5aR,7aS,11S,11aS,11bR,14S)-1,7,7a,11,11a,11b-hexahydro-1,11-dihydroxy-8,11a,14-trimethyl-2H-5a,2,5-(methanoxymetheno)naphth[1,2-d]oxepine-4,6,10(5H)-trione, C(19)H(22)O(7), and samaderin C, or (1R,2S,5R,5aR,7aS,10S,11S,11aS,11bR,14S)-7,7a,10,11,11a,11b-hexahydro-1,10,11-trihydroxy-8,11a,14-trimethyl-2H-5a,2,5-(methanoxymet...
Article
The title compound, dimethyl (-)-(2aR,3R,4R,4aS,5R,7aS,8R,10S,10aR)-3,8,10-trihydroxy-4-[(2R,6R)-2-hydroxy-11-methyl-5,7,10-trioxatetracyclo[6.3.1.0(2,6)0(9,11)]dodec-3-en-9-yl]-4-methylperhydroisobenzofurano[5,4,3a-cd]isobenzofuran-5,10a-diacetate, C(28)H(36)O(13), which exhibits higher antifeedant activity than azadirachtin-A, a known potent anti...
Article
The 11 ß-H epimer of Azadirachtin-I, isolated from the seed kernels of Azadirachta indica A. Juss (Neem), was characterized by both NMR and X-ray crystallographic techniques. NMR data reveals that the H11 proton is in ß-orientation and the X-ray studies confirm this observation. The compound crystallized in space group P21 with the cell parameters...
Article
The title compound, C(16)H(19)BrO(4), is a derivative of osthol, isolated from the seeds of Imperatoria Osthruthium. The structure was solved in space group P-1, with two molecules in the asymmetric unit, and was refined to a final R factor of 0.064. The two molecules in the asymmetric unit differ in the orientation of their brominated substituent...
Article
The title compound, methyl (2aS,3R,5R,5aS,6S,6aS,8R,9aS,10aR,10bR,10cS)-8-(3-furyl)-2a,4,5,5a,6,6a,8,9,9a,10a,10b,10c-dodecahydro-3-hydroxy-2a,5a,6a,7-tetramethyl-5-(3-methylbut-2-enoyloxy)-2H,3H-cyclopenta[4',5']furo[2',3':6,5]benzo[cd]isobenzofuran-6-acetate, C(32)H(42)O(8), was isolated from uncrushed green leaves of Azadirachta indica A. Juss (...
Article
Structure-related insect antifeedant relationship of 56 limonoids (both natural and modified) from the plants belonging to the order Rutales was attempted considering substitution patterns, oxidation states, and hydrophobicity, as well as distant geometry derived through conformational analysis on molecular modeling. Orientation of the furan and hy...
Article
Full-text available
A facile regio- and chemoselective bromomethoxylation of alkenes under microwave irradiation conditions employing a new polymer supported brominechloride resin is reported. The resin is prepared from the commercially available chloride resin by a simple one step procedure.
Article
[reaction: see text] A novel procedure for the preparation of 3-(4-alkoxyphenyl)-3-methylbutan-2-one in excellent yield is described via polymer-supported AlCl3-catalyzed rearrangement of 1-(4-ethoxyphenyl)-2,2-dimehtylpropan-1-one, followed by O-alkylation under microwave irradiation condition.
Article
The crystal structures of two cinnamanilide derivatives 2-methyl cinnamanilide (C16 H15 N O – compound I) and 2-methoxy cinnamanilide (C16 H15 N O2 – compound II) are reported. In both crystal structures, the cinnamamide group is almost planar. The inter-planar angle between the two phenyl rings are 71.6(1)° for compound I and 7.5(1)° for compound...
Article
Full-text available
Nimonol (1), a tetranortriterpenoid isolated from the leaves of Azadirachta indica A. Juss (Meliaceae), upon photolysis undergoes both Diels-Alder and ene reactions with singlet oxygen at different sites leading to 14,15,20,21-diepoxy-23-nimonolactone (3), along with nimonolide (4), which have been well-characterised. The novelty of the reported re...
Article
Tetranortriterpenoids from Azadirachta indica A. Juss and Soymida febrifuga (Meliaceae), have been selectively oxidized to single major products which exhibit bioactivity higher than the parent compounds, comparable to that of azadirachtin A. The reaction proceeds to completion in less than 15 min and 1 min on being assisted by ultrasound and micro...
Article
Four quassinoids, indaquassin C (1), samaderins C (2), B (3) and A (4), isolated from the seeds and bark of Samadera indica, were tested for insect antifeedant and growth regulatory activities against the tobacco cutworm, Spodoptera litura. Indaquassin C was the most effective antifeedant. Samaderin C increased pupal duration and induced pupal mort...
Article
Full-text available
Photolysis of Salannin (1), an important bioactive compound from Azadirachta indica A.Juss (Neem), affords Δ17-isosalanninolide (2), a hitherto unknown compound, along with isosalanninolide (3) and salanninolide (4). A probable mechanism has been suggested. While the mechanism of formation of 2 involves both a [4+2] cycloaddition and a [1,3] sig...
Article
Cedrelone, a tetranortriterpenoid on photolysis by UV light yields a true photooxidation product 3 [14 beta,15beta,22beta,23beta-diepoxy-6-hydroxy-1,5, 20(22)-meliatriene-2,7,21-trione] whose structure is well established by NMR studies and confirmed by X-ray crystallography, along with product 4 [14 beta,15beta-epoxy-6,23-dihydroxy-1,5,20(22)-meli...
Article
Natural tetranortriterpenoids such as cedrelone from Toona ciliata, azadiradione from Azadirachta indica, limonin, limonol and nomilinic acid from Citrus medica, along with some cedrelone derivatives were tested for their antifungal activity against Puccinia arachidis, a groundnut rust pathogen. Results show that cedrelone was the most effective in...
Article
Full-text available
A tandem demethylation-cyclisation reaction resulting in the formation of pyran rings using AlCl3/EtSH reagent under mild reaction conditions is reported. X-ray diffraction studies on the intermediate support the suggested mechanism.
Article
A quantitative HPLC analysis of the major triterpenoids present in an aqueous extract of powdered neem kernels prepared in the traditional manner was undertaken. The study shows that water extracts contain all the principal triterpenoids in neem kernel though the quantities extracted are much less than in the subsequent extraction with methanol.
Article
The crystal structures of two tetranortriterpenoids, salannin [C34H44O9, (I)] and 3-deacetylsalannin [C32H42O8, (II)], are described. The orientation and conformation of the tigloyl (2-methyl-2-butenoyl) group, the carbomethoxy group and ring E are different in the two structures. The molecular packing depends on C - H⋯O hydrogen bonds in (I) and o...
Article
14,15-Epoxynimonol, a new tetranortriterpenoid, was obtained from the fresh green whole leaves of Azadirachta indica and its structure has been assigned on the basis of spectral data. The 14,15-epoxide was assigned β-configuration by comparison with cedrelone.
Article
The spectral data of the crystalline samples of 11α-H and 11β-H epimers of Azadirachtin H is presented. 11α-H epimer is converted to the 11β-H epimer under extremely mild conditions while the reverse conversion cannot be achieved.
Article
Isolation and characterization of B,D-seco limonoids from Swietenia mahogani have been described. Seven limonoids from S. mahogani and five limonoids from Khaya senegalensis were tested for antifungal activity against the groundnut rust Puccinia arachidis. Mexicanolide, 3-acetoxy-mexicanolide, 3-hydroxymexicanolide, 2,3-dihydroxymexicanolide from K...
Article
Evaluation of the activity of the cold expeller neem oil(Azadirachta indica A. Juss.) and the fractions derived through solvent partitioning, againstDrechslera oryzae, Fusarium oxysporum andAlternaria tenuis showed that the active antifungal fraction is a mixture of tetranortriterpenoids. Further, testing the triterpenoidal mixture derived from the...
Article
The crystal structure of nimbin has been determined. The crystals are orthorhombic, space groupP212121 witha=6.790(2),b=14.875(4),c=27.160(8) andZ=4. The packing of the molecules in the lattice is due to C−H…O type of hydrogen bonds.
Article
The antifungal activity of several xanthones isolated from the fruit hulls of Garcinia mangostana and some derivatives of mangostin against three phytopathogenic fungi, Fusarium oxysporum vasinfectum, Alternaria tenuis, and Dreschlera oryzae, has been evaluated. The natural xanthones showed good inhibitory activity against the three fungi. Substitu...
Article
Isolation of Azadirachtin-B in pure form suitable for crystallisation from neem seed kernel extract by a preparative high performance liquid chromatography followed by a subsequent preparative HPLC using the recycling mode is described.
Article
A new tetranortriterpenoid, 13,14-desepoxyazadirachtin-A, has been isolated from neem kernel extract by preparative HPLC and its structure established by spectroscopic methods.
Article
Using the groundnut rust disease (causal agentPuccinia arachidis Speg.) as the bioassay system, two limonoids from the neem tree (Azadirachta indica A. Juss.) which evinced antifungal activity, were isolated through extraction, solvent fractionation and HPLC. A polar extract derived through solvent partitioning reduced the disease intensity conside...
Article
Full-text available
The antifeedant and insect growth-regulating activities of salannin, nimbin, and 6-deacetylnimbin, in comparison with azadirachtin-A, have been studied againstSpodoptera litura, Pericallia ricini, andOxya fuscovittata. Salannin deterred feeding, delayed molt by increasing larval duration, caused larval and pupal mortalities, and decreased pupal wei...
Article
Isolation of various azadirachtins, ie., Azadirachtin A, B, D, H and I in pure form from neem oil by preparative high performance liquid chromatography procedure is described.
Article
Azadirachtin-H, isolated from the seed kernels of Azadirachta indica (neem), crystallizes in space group I4, Z = 8, with disordered ethyl acetate solvent filling channels along the fourfold rotation axes. The crystal structure determination showed that the previously reported molecular structure deduced from NMR studies was correct except for the s...
Article
A new route to the synthesis of 2-(4-ethoxyphenyl)-2-methyl-5-(3-phe-noxyphenyl)pentane (desfluoro MTI-800) and 2-(4-ethoxyphenyl)-2-methyl-5-(4-fluoro-3-phenoxyphenyl)pentane (MTI-800) and the insecticidal activities of these compounds and some of the synthetic intermediates against the tobacco caterpillar Spodoptera litura (F.) is reported.
Article
Isolation of the major triterpenoids from neem oil in pure form by a direct preparative High performance liquid chromatography procedure is presented. As neem oil is an important component of Neem based insecticidal formulations, a simple, isocratic analytical HPLC procedure for quantitation (relative abundance) of these major bioactive triterpenoi...
Article
Insect antifeedant and growth-regulating activities of 22 limonoids (both natural and their derivatives) againstSpodoptera litura were studied to understand the structure-related bioactivities of the limonoids. The C-seco limonoids (azadirachtins A, B, D, H, and I) were the most effective compounds as a group, while the intact limonoids (cedrelone...