Shreyans K. Jain

Cyclin-dependent kinase inhibition by flavoalkaloids.

Chromone alkaloids and flavoalkaloids are an important group of natural products possessing promising medicinal properties. A chromone alkaloid rohitukine is a major bioactive chemical constituent of plant Dysoxylum binectariferum (Meliaceae) Hook. which is phylogenetically related to the Ayurvedic plant, D. malabaricum Bedd. used for treatment of rheumatoid arthritis. This chromone alkaloid led to discovery of two synthetic flavoalkaloids: flavopiridol (Sanofi) and P-276-00 (Piramal) which have reached to advanced stages of clinical development for cancer treatment. Flavopiridol (Alvocidib; L868275; HMR-1275; NSC 649890 of Sanofi-Aventis + NCI) is approved as an orphan drug for treatment of chronic lymphocytic leukemia and is currently undergoing phase II studies as monotherapy and also as in combination regimes with traditional chemotherapy agents. P-276-00 (12) is currently in phase II clinical studies for advanced refractory neoplasms and multiple myeloma. Extensive amount of medicinal chemistry efforts have been reported on these flavoalkaloids. Flavopiridol demonstrated potent and specific in vitro inhibition of variety of cyclindependent kinases with clear block in cell cycle progression at the G1/S and G2/M phases. Preclinical studies demonstrated the capacity of flavopiridol to induce programmed cell death, promote differentiation, inhibit angiogenic processes and modulate transcriptional events. The co-crystallised structure of deschloro-flavopiridol with CDK-2 is available and key interactions in the ATP binding site have been reported. Flavopiridol has also been studied for the treatment of arthritis and atherosclerotic plaque formation. The present review comprises discovery, medicinal chemistry, pharmacology and preclinical/clinical development of flavoalkaloids as CDK inhibitors.

Synthesis and Antileishmanial activity of Piperoyl-Amino Acid Conjugates

Based on reported antileishmanial activity of naturally occurring alkaloid piperine and amino acid esters, their conjugates were synthesized by the hydrolysis of piperine to piperic acid followed by reaction with amino acid methyl esters. These conjugates were further converted to compounds with free carboxyl group and those with reduced double bonds. The synthesized compounds were evaluated for activity against promastigote and amastigote forms of L. donovani in vitro. All the compounds showed better activity than either piperine or the amino acid methyl esters. Piperoyl-valine methyl ester was the most active compound showing an IC50 of 0.075 mM against the amastigotes. Two active compounds were evaluated for in vivo activity in golden hamster model of leishmaniasis.

Cu–Mn spinel oxide catalyzed synthesis of imidazo[1,2-a]pyridines through domino three-component coupling and 5-exo-dig cyclization in water

An efficient and eco-friendly synthesis of therapeutically important and structurally diverse imidazo[1,2-a]pyridines using recyclable bimetallic Cu–Mn spinel oxide catalyst in aqueous medium has been developed. The Cu–Mn catalyzed domino three-component coupling of 2-aminopyridines, aldehydes and alkynes followed by 5-exo-dig cycloisomerization produced desired imidazo[1,2-a]pyridines in good yields. The efficiency of this protocol could be attributed to the presence of these metals in multiple oxidation states (Cu2+, Mn2+, Mn3+ and Mn4+) in the bimetallic Cu–Mn catalyst. The advantages of this protocol over previous reports include the use of aqueous medium, recyclable catalyst, shorter reaction times and no requirement of any additive. This is the first method for synthesis of imidazo[1,2-a]pyridines which utilizes water as a reaction medium.

ortho-Amidoalkylation of Phenols via Tandem One-Pot Approach Involving Oxazine Intermediate

A new and efficient method for ortho-amidoalkylation of phenols via Mannich-type condensation with formaldehyde and lactams using recyclable solid acid catalyst is described. This is the first report for ortho-amidoalkylation of phenols by lactams via Mannich-type condensation. LC-ESI-MS/MS based mechanistic study revealed that reaction proceeds through o-quinone methide (o-QM) and an oxazine intermediate via tandem Knoevenagel condensation, formal [4 + 2]-Diels-Alder cycloaddition and acid catalyzed oxazine ring-opening.

Osthol and curcumin as inhibitors of human Pgp and multidrug efflux pumps of Staphylococcus aureus: reversing the resistance against frontline antibacterial drugs

The in-house IIIM natural product repository of 302 small molecules was screened for their ability to inhibit P-glycoprotein (Pgp) in Pgp-overexpressing human adenocarcinoma LS-180 cells. The screening has identified 13 natural products displaying significant Pgp-inhibition activity, which include praeruptorin B, curcumin, imperatorin, osthol, 5,7-diacetoxy-8-(3-methyl-2-butenyl)-coumarin, 5,7-dihydroxy-8-(3-methyl-2-butenyl) coumarin, pongamol, phellopterin, tangeretin, 3-(2-methyl but-3-en-2-yl) xanthyletin, 7-demethyl osthol, allorottlerin and tetrahydroangeolide. These natural products were then screened for their effects on bacterial efflux pump inhibition activity against NorA (Staphylococcus aureus), MdeA (S. aureus Mupr-1), TetK (S. aureus SA-K2192), and MsrA (S. aureus SA-K2191) efflux pumps. Curcumin and osthol showed significant inhibition of the S. aureus NorA efflux pump with 8- and 4-fold reductions in the MIC of ciprofloxacin at 25 μM. The molecular docking studies of curcumin and osthol with the human Pgp and S. aureus NorA efflux pump identified plausible binding modes and binding sites for these natural products.

Dysoxylum binectariferum bark as a new source of anticancer drug camptothecin: Bioactivity-guided isolation and LCMS-based quantification

Camptothecin (CPT, 1) is a potent anticancer natural product which led to the discovery of two clinically used anticancer drugs topotecan and irinotecan. These two drugs are semisynthetic analogs of CPT, and thus the commercial production of CPT as a raw material from various plant sources and tissue culture methods is highly demanding. In the present study, the Dysoxylum binectariferum bark, was identified as an alternative source of CPT, through bioassay-guided isolation. The barks showed presence of CPT (1) and its 9-methoxy analog 2, whereas CPT alkaloids were not present in seeds and leaves. This is the first report on isolation of CPT alkaloids from Meliaceae family. An efficient chromatography-free protocol for enrichment and isolation of CPT from D. binectariferum has been established, which was able to enrich CPT up to 21% in the crude extract. The LCMS (MRM)-based quantification method revealed the presence of 0.105% of CPT in dry barks of D. binectariferum. The discovery of CPT from D. binectariferum bark will certainly create a global interest in cultivation of this plant as a new crop for commercial production of CPT. Isolation of anticancer drug CPT from this plant, indicates that along with rohitukine, CPT and 9-methoxy CPT also contributes significantly to the cytotoxicity of D. binectariferum.

Pyrano-isochromanones as IL-6 inhibitors: synthesis, in vitro and in vivo antiarthritic activity.

Bergenin (1), a unique fused C-glycoside isolated from Bergenia species, possesses interesting anti-inflammatory and antipain activities. To study SAR of this scaffold, first-generation derivatives were synthesized and evaluated for inhibition of lymphocyte proliferation and production of pro-inflammatory cytokines. The C-7 substituted derivatives showed inhibition of IL-6 as well as TNF-α production. Bergenin and its most potent IL-6 inhibitor derivatives 4e and 4f were then investigated in a panel of in vitro and in vivo inflammation/arthritis models. These compounds significantly decreased the expression of NF-kB and IKK-β in THP-1 cells. In in vivo study in BALB/c mice, a dose-dependent inhibition of SRBC-induced cytokines, reduction in humoral/cell-mediated immunity, and antibody titer was observed. The CIA study in DBA/1J mice indicated that compounds led to reduction in swelling of paws, cytokine levels, and anticollagen IgG1/IgG2a levels. The significant in vivo immunosuppressive efficacy of pyrano-isochromanones demonstrates the promise of this scaffold for development of next-generation antiarthritic drugs.

An Insight into the Secondary Metabolism of Muscodor yucatanensis: Small-Molecule Epigenetic Modifiers Induce Expression of Secondary Metabolism-Related Genes and Production of New Metabolites in the Endophyte

Muscodor spp. are proficient producers of bioactive volatile organic compounds (VOCs) with many potential applications. However, all members of this genus produce varying amounts and types of VOCs which suggests the involvement of epigenetics as a possible explanation. The members of this genus are poorly explored for the production of soluble compounds (extrolites). In this study, the polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) genes from an endophyte, Muscodor yucatanensis Ni30, were cloned and sequenced. The PKS genes belonged to reduced, partially reduced, non-reduced, and highly reduced subtypes. Strains over-expressing PKS genes were developed through the use of small-molecule epigenetic modifiers (suberoylanilide hydroxamic acid (SAHA) and 5-azacytidine). The putative epigenetic variants of this organism differed considerably from the wild type in morphological features and cultural characteristics as well as metabolites that were produced. Each variant produced a different set of VOCs distinct from the wild type, and several VOCs including methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)hexane-2,4-diol and 2-carboxymethyl-3-n-hexylmaleic appeared in the variant strains, the production of which could be attributed to the activity of otherwise silent PKS genes. The bioactive extrolite brefeldin A was isolated and characterized from the wild type. However, this metabolite was not detected in EV-1, but instead, two other products were isolated and characterized as ergosterol and xylaguaianol C. Hence, M. yucatanensis has the genetic potential to produce several previously undetectable VOCs and organic solvent soluble products. It is also the case that small-molecule epigenetic modifiers can be used to produce stable variant strains of fungi with the potential to produce new molecules. Finally, this work hints to the prospect that the epigenetics of an endophytic microorganism can be influenced by any number of environmental and chemical factors associated with its host plant which may help to explain the enormous chemical diversity of secondary metabolic products found in Muscodor spp.

A chromatography-free isolation of rohitukine from leaves of Dysoxylum binectariferum: Evaluation for in vitro cytotoxicity, Cdk inhibition and physicochemical properties.

Rohitukine is a chromone alkaloid isolated from an Indian medicinal plant Dysoxylum binectariferum. This natural product has led to the discovery of two clinical candidates (flavopiridol and P276-00) for the treatment of cancer. Herein, for the first time we report an efficient protocol for isolation and purification of this precious natural product in a bulk-quantity from leaves (a renewable source) of D. binectariferum (>98% purity) without use of chromatography or any acid-base treatment. Despite of the fact that this scaffold has reached up to clinical stage, particularly for leukemia; however the antileukemic activity of a parent natural product has never been investigated. Furthermore, rohitukine has never been studied for cyclin-dependent kinase (Cdk) inhibition, kinase profiling and for its experimental physicochemical properties. Thus, herein, we report in vitro cytotoxicity of rohitukine in a panel of 20 cancer cell lines (including leukemia, pancreatic, prostate, breast and CNS) and 2 normal cell lines; kinase profiling, Cdk2/9 inhibition, and physicochemical properties (solubility and stability in biological medias, pKa, LogP, LogD). In cytotoxicity screening, rohitukine displayed promising activity in HL-60 and Molt-4 (leukemia) cell lines with GI50 of 10 and 12μM, respectively. It showed inhibition of Cdk2/A and Cdk9/T1 with IC50 values of 7.3 and 0.3μM, respectively. The key interactions of rohitukine with Cdk9 was also studied by molecular modeling. Rohitukine was found to be highly water soluble (Swater=10.3mg/mL) and its LogP value was -0.55. The ionization constant of rohitukine was found to be 5.83. Rohitukine was stable in various biological medias including rat plasma. The data presented herein will help in designing better anticancer agents in future.

Chrysomycins A–C, antileukemic naphthocoumarins from Streptomyces sporoverrucosus

Two known naphthocoumarins, chrysomycins A (1) and B (2), along with one new naphthocoumarin chrysomycin C (3) were isolated from the antimicrobial strain of Streptomyces sporoverrucosus (MTCC11715) (isolated from soil samples from the Jammu hills) and characterized. The structure of the new compound 3 was established from 2D-NMR data. Chrysomycins A (1) and B (2) were identified using a strategic HPLC–PDA/LCMS and Dictionary of Natural Products (DNP) based fast dereplication. Additionally, two new naphthocoumarins, chrysomycins D and E were identified using LCMS, UV and DNP information. Chrysomycins A–C (1–3) were isolated for the first time from Streptomyces sporoverrucosus and were screened for cytotoxicity against a panel of cancer cell lines (A549, Colo205, PC-3, MIAPaCa-2, and HL-60), amongst which the most potent activity was observed against human leukemia HL-60 cells with IC50 values of 0.9, 0.95 and 11 μM, respectively. The mechanistic studies indicated that chrysomycins A (1) and B (2), at 1 μM concentration, distorted the cellular and nuclear morphology with significant DNA damage and apoptosis in HL-60 cells.