K. Rajendra Prasad

Methyl angolensate and mexicanolide-type limonoids from the seeds of Cipadessa baccifera.

Six new methyl angolensate type (1-6) and three new mexicanolide-type (7-9) limonoids, along with six known limonoids (10-15), were isolated from the seeds of Cipadessa baccifera. The structures of all these compounds were established by extensive 1D, 2D NMR, and HRESIMS experiments, and structures of 11 and 13 were further confirmed by a single crystal X-ray diffraction analysis, which are reported for the first time. The cytotoxic activities of these isolates were also studied against A549, MCF7, ME-180, HT-29, B-16, ACHN cancer cell lines using MTT assay, and results indicated that compounds 4, 10, and 14 displayed potent cytotoxic activity against B-16, ACHN cell lines with an IC50 values of 8.51 and 7.0 μg/mL, respectively.

Phytochemical investigation of sesquiterpenes from the fruits of Schisandra chinensis and their cytotoxic activity.

Phytochemical investigation of ethanolic extract from the fruits of Schisandra chinensis led to the isolation of four new sesquiterpenes (1-4); their structures were determined by a combination of NMR (1D and 2D) and MS spectroscopic techniques. In addition, all these isolates were screened for their cytotoxic activities against MCF-7, Caco-2, Hela, Lncap, Hep G2 and MDA-MB231 cancer cell lines. Results indicated that compounds 2 and 3 displayed potent cytotoxic activity against Caco2 cell lines with IC50 values of 17.10 μg/mM and 16.46 μg/mM, respectively.

Cytotoxic sesquiterpenes from Hedychium spicatum: isolation, structure elucidation and structure-activity relationship studies.

Phytochemical investigation of chloroform extract from rhizomes of Hedychium spicatum resulted in the isolation of six new sesquiterpenes (1-6) along with fifteen known compounds (7-21). Their structures were elucidated on the basis of the extensive spectroscopic analyses (IR, Mass and NMR) and by comparison of the data with those reported in the literature. Further, cytotoxic activities of all the isolates were evaluated by determining their inhibitory effects against A-549, B-16, Hela, HT-29, NCI-H460, PC-3, IEC-6 and L-6 cancer cell lines. Results indicated that compounds 1 and 3 may serve as an important natural lead compounds for future development as they showed potent cytotoxic activity against Hela cell lines with an IC50 value of 0.3 μg/mL and 1.80 μg/mL, respectively.

Synthesis and insect antifeedant activity of plumbagin derivatives

Napthaquinones have received considerable interest in agricultural chemistry because of a novel action mode, extremely high activity against a broad spectrum of insects, low acute toxicity to mammals, and environmentally benign characteristics. A series of plumbagin derivatives (3a–3o) were synthesized under mild esterification conditions in straightforward procedure. The structures of all new compounds were confirmed by NMR, IR, MS, and HREIMS analyses. The plumbagin derivatives were screened for their insecticidal activities against tobacco caterpillar (Spodoptera litura) and castor semilooper (Achaea janata) using a no-choice laboratory bioassay. The results show that some of the title compounds exhibit excellent antifeedant activities against 3rd instar larvae of A. janata and S. litura. The improvement in antifeedant activity requires a reasonable combination of substituents in the parent structure, which provides some hints for further investigation on structure modification.Graphical AbstractA series of plumbagin derivatives (3a–3o) were synthesized under mild conditions and screened for their insecticidal activities against tobacco caterpillar (Spodoptera litura) and castor semilooper (Achaea janata) using a no-choice laboratory bioassay.

New advanced glycation end-products inhibitors from Dichrostachys cinerea Wight & Arn.

Free radical scavenging and advanced glycation end-product (AGE) inhibitory potential were evaluated in the crude methanol extract of Dichrostachys cinerea. Bioassay-guided isolation led to the identification of four flavan-3-ols, namely (−)-mesquitol (1), oritin (2), (−)-festidinol (3) and (−)-epicatechin (4). Analysis of structure–activity relationships revealed that the presence of 7,8-dihydroxyl groups in the A-ring of flavan-3-ols in conjunction with 3′,4′-dihydroxyls in the B-ring (1) is an important criterion for displaying potent AGE inhibitory activity along with free radical scavenging properties. (−)-Mesquitol (1), oritin (2), and (−)-festidinol (3) were found to be new natural AGE inhibitors. (−)-Mesquitol (1) displayed the most potent AGE inhibitory activity. Results suggest that (−)-mesquitol (1) may serve as an important natural organic lead compound for future development of antiglycating agents along with potent antioxidant activity.

Synthesis and biological evaluation of novel benzyl-substituted flavones as free radical (DPPH) scavengers and α-glucosidase inhibitors

Pharmacologically motivated natural product investigations have yielded a large variety of structurally unique lead compounds with interesting biomedical properties, but the natural roles of these molecules often remain unknown. In the present investigation, a series of benzyl substituted-flavone derivatives have been synthesized from the lead compounds and were screened against 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging and α-glucosidase inhibitory properties. The resulting activity profiles of these flavone derivatives were compared for degree of similarity to the profile of 1–3. Most of the synthesized derivatives displayed potent activities when compared to the parent compounds. Maximum potencies for DPPH free radical scavenging activity were observed only in compounds containing the 4-hydroxyl substitution and 3-methoxyl group on the phenyl ring. While the 2- and 4-hydroxyl group substitutions on the phenyl ring seem to be crucial for the intestinal α-glucosidase inhibitory activity.