Halmuthur M. Sampath Kumar

Design, Synthesis, and Biological Testing of 4β-[(4-Substituted)-1,2,3-triazol-1-yl]podophyllotoxin Analogues as Antitumor Agents

A series of 4β‐[(4‐substituted)‐1,2,3‐triazol‐1‐yl]podophyllotoxin analogues have been synthesized with high regio‐selectivity by employing copper(I)‐catalyzed 1,3‐dipolar cycloaddition of 1‐O‐propargyl monosaccharides with C4β‐azido podophyllotoxin and C4β‐azido‐4′‐O‐demethyl podophyllotoxin. All the compounds were evaluated for their anticancer activity against a panel of six human cancer cell lines. Among these, 4′‐O‐demethyl podophyllotoxin congeners are showing promising anticancer activity mainly against HCT‐15 (colon) and DU‐145 (prostate) cells.

Design, Synthesis, and Immunological Evaluation of Benzyloxyalkyl-Substituted 1,2,3-Triazolyl α-GalCer Analogues.

Replacement of the amide moiety in the structure of α-GalCer with a 1,2,3-triazole linker is known to elicit a response skewed toward Th2 immunity, and glycolipids containing an aromatic ring in the terminus of their acyl or phytosphingosine structural component exhibit an enhanced Th1 immune response. In the current study, synthesis and immunological screening of a focused library of benzyloxyalkyl-substituted 1,2,3-triazolyl α-GalCer analogues are reported. The novel α-GalCer analogues activate invariant natural killer T (iNKT) cells via CD1d mediated presentation, which was confirmed by in vitro tests performed on iNKT hybridomas incubated with CD1d proteins. When tested on isolated murine splenocytes, the T1204B and T1206B compounds stimulated higher levels of both IFN-γ and IL-4 cytokine expression in vitro compared to that of α-GalCer.

Synthesis and Biological Evaluation of 4β-[(4-Substituted)-1,2,3-triazol-1-yl]podophyllotoxins as Potential Anticancer Agents

A series of novel 4β‐[(4‐substituted)‐1,2,3‐triazol‐1‐yl]podophyllotoxin derivatives were synthesized by employing CuI‐catalyzed click chemistry and evaluated for their anticancer activity against a panel of seven human cancer cell lines (HT‐29, HCT‐15, 502713, HOP‐62, A‐549, MCF‐7, and SF‐295). The compounds 9b, 9c, 9e, 9f, and 9h showed significant cytotoxic activities especially against HT‐29, HCT‐15, 502713 cell lines.

Design and synthesis of novel 1,2,3-triazole derivatives of coronopilin as anti-cancer compounds.

A series of 1,2,3-triazole coronopilin congeners have been designed and synthesized by employing click chemistry approach starting from parthenin and evaluated for their cytotoxicity against a panel of six human cancer cell lines (PC-3, THP-1, HCT-15, HeLa, A-549 and MCF-7). While many compounds exhibited significant anticancer activity, compound 3a, was found to be the most promising analogue in this series with IC50 values of 3.1 μM on PC-3 cell line. Flow-cytometric studies showed that 1,2,3-triazole derivative-3a induce dose dependent apoptosis in the sub G1 phase. This lead molecule-3a was further studied for NF-κB (p65) transcription factor inhibitory activity using Elisa and western blotting analysis which confirmed concentration dependent inhibitory activity against NF-κB, p65 with 80% inhibition in 24 h at 100 μM.

Synthesis and Biological evaluation of novel 4β-[(5-substituted)-1,2,3,4-tetrazolyl] podophyllotoxins as anticancer compounds.

A series of novel 4β-[(5-substituted)-1,2,3,4-tetrazolyl] podophyllotoxin derivatives were synthesized by employing azide-nitrile click chemistry approach. All the derivatives were evaluated for their cytotoxicity against a panel of four human cancer cell lines and their IC50 values were found to be in the range of 2.4-29.06 μM. The cytotoxicity exhibited by the majority of test compounds were found to comparable and often more effective than doxorubicin and all compounds exhibited higher cytotoxicity on A-549 cell lines. Cell cycle analysis showed that the novel 4β-[(5-substituted)-1,2,3,4-tetrazolyl] podophyllotoxins resulted in cell cycle arrest at G2/M phase and were also found to be the potent inhibitors of tubulin polymerization in vitro.

Free radical addition of haloalkanes to polymer bound olefins and its application to the solid-phase synthesis of pyrethroids

Polymer bound olefins undergo free radical initiated 1,2-addition when reacted with a variety of haloalkanes. The strategy could be applied successfully to the solid-phase synthesis of dihaloethenylcyclopropane carboxylic acids which are the key fragments of synthetic pyrethroids.

Synthesis and immunopotentiating activity of novel isoxazoline functionalized coumarins

A novel series (13) of isoxazoline functionalized coumarins was synthesized through 1,3-dipolar cyclization of nitrile oxides with Allylated coumarins. Synthesis of effective and target selective immunostimulators through conjugation of diversely substituted isoxazolines and 7-hydroxycoumarins is the focus of the present article. The proposed synthetic scheme was observed to be highly regiospecific yielding attempted conjugates in good yield (>90%). Kinetic resolution of the racemates was carried out by employing lipase B from Candida antarctica (CALB). The synthesized compounds were screened inxa0vitro and inxa0vivo for their biological activities viz. toxicity and impact on splenocyte proliferation (T- and B-cell proliferation), antibody production (HA titre), delayed-type hypersensitivity reaction (DTH), T-cell subtypes (CD4 and CD8), cytokine production (IL-2, IFN-γ, and IL-4) and NO (macrophage) production. Our results establish that isoxazoline functionalized coumarins exhibit excellent immune potentiating activity especially compounds 2, 4 and 8 whose activity is more than that of Levimasole as standard. The structure activity relations are explained in light of the structural/functional aspects of tested compounds. To the best of our knowledge the presented work is first of its kind and is presaged to prove very useful for the design and synthesis of bis-heterocycle based novel, therapeutically selective and effective immunopotentiators.

Synthesis and tyrosinase inhibition activity of trans-stilbene derivatives

Synthesis of a focussed library of trans-stilbene compounds through Wittig and other base catalysed condensation reactions is presented. The synthesized stilbenes were screened for their inhibitory potential against murine tyrosinase activity to explore the structure activity relationship (SAR). Presence of electron withdrawing group (-CN) at the double bond and hydroxyl group or halogen atom especially at para-position on the aromatic rings was found to significantly elevate the inhibitory activity. Among all the compounds screened, compounds 2, 6, 8, 10, 11, 15 and 21 were found to exhibit appreciable inhibitory activity. Compound 21 ((E)-2,3-bis(4-Hydroxyphenyl)acryonitrile) was found to be the most active with an IC50 value of 5.06 μM which is less than half of the value 10.78 μM observed for resveratrol (common standard used in murine tyrosinase activity studies) under similar conditions. The results obtained from the present study reveal structural/functional group sensitivity for the tyrosinase inhibitory activity of stilbenoid moieties and are expected to be very helpful for the design and synthesis of novel, selective and effective tyrosinase inhibitors.

Enzyme mediated-transesterification of verbascoside and evaluation of antifungal activity of synthesised compounds

Enzymatic acylation of verbascoside, a polyhydroxylated natural product, has been reported in this study using five different commercial lipases and taking p-nitrophenyl alkanoates as acyl donors. Out of these enzymes, the immobilised Candida antarctica lipase B was found as the enzyme of choice. Mono- and di-acylated products were formed, with mono as major product indicating high regioselective nature of such transformations. A series of acyl esters of verbascoside have been synthesised by this enzymatic transesterification methodology. The lipophilicity of the synthesised analogues was also checked. The analogues were further subjected to synergistic antifungal activity with amphotericin B (AmB) against Candida albicans. Fourfold reduction in minimum inhibitory concentration of AmB was observed with few synthesised analogues such as verbascoside 4″-octanoate (3b), verbascoside 4″-palmitate (3d) and verbascoside 4″,4′-dipalmitate (4d) at a concentration of 0.5 μg/mL.

Synthesis of novel lipidated iridoid glycosides as vaccine adjuvants: 6-O-Palmitoyl Agnuside elicit strong Th1 and Th2 response to ovalbumin in mice

Novel lipidated analogs of iridoids viz., Agnuside and Negundoside with different chain length were synthesized and tested for immune adjuvant activity in the presence of weak antigen ovalbumin. Based on in vitro assay, 6-O-palmitoyl Agnuside (AG-3) was further taken up for detailed in vivo activity and found to significantly enhance the production of anti OVA IgG titer, neutralizing antibody (IgG1 and IgG2a) titer as well as soluble mediators of a Th1 (IL-2, IFN-γ)/Th2 response (IL-4) and proliferation of T lymphocyte subsets (CD4/CD8) and co stimulatory molecules CD80/CD86. Furthermore, the SAR studies revealed that presence of acyl group at aglycon moiety of these iridoid glycosides is crucial for immune adjuvant activity.