Syntheses and bioactivities of macrocyclic paclitaxel bis-lactones

Macrolactonization Reactions Driven by a Pentafluorobenzoyl Group*

Macrolactones constitute a privileged class of natural and synthetic products with a broad range of applications in the fine chemicals and pharmaceutical industry. Despite all the progress made towards their synthesis, notably from seco-acids, a macrolactonization promoter system that is effective, selective, flexible, readily available, and, insofar as possible, compatible with manifold functional groups is still lacking. Herein, we describe a strategy that relies on the formation of a mixed anhydride incorporating a pentafluorophenyl group which, due to its high electronic activation enables a convenient access to macrolactones, macrodiolides and esters with a broad versatility. Kinetic studies and DFT computations were performed to rationalize the reactivity of the pentafluorophenyl group in macrolactonization reactions.

In-vitro and in-silico anticancer potential of taxoids from Taxus wallichiana Zucc

INTRODUCTION

Natural products derived from medicinal plants provide beneficial cancer chemotherapeutic drugs. Bioactive constituents from plants are explored for their anticancer properties.

METHODS

Three known compounds (deacetylbaccatin III, tasumatrol B, and taxawallin J) were isolated from Taxus wallichiana. Compounds were screened against four cancer cell lines, such as eA498, HepG2, NCI-H226, and MDR 2780AD. Cytotoxic activity was evaluated using MTT assay against cancer cell lines.

RESULTS

Tasumatrol B showed good cytotoxic activity conducted for the improvement of inhibiting potential of these compounds against the cancer drug target protein (EGFR tyrosine kinase enzyme). The docking study showed that all compounds have binding affinities and interaction profile with the receptor tyrosine kinase.

DISCUSSION

The study suggests that these compounds could be used for the discovery of novel inhibitors against the target receptors for the treatment of cancer.

Paclitaxel Biosynthesis: Adenylation and Thiolation Domains of an NRPS TycA PheAT Module Produce Various Arylisoserine CoA Thioesters

Structure-activity relationship studies show that the phenylisoserinyl moiety of paclitaxel (Taxol) is largely necessary for the effective anticancer activity. Several paclitaxel analogues with a variant isoserinyl side chain have improved pharmaceutical properties versus those of the parent drug. To produce the isoserinyl CoAs as intermediates needed for enzyme catalysis on a semibiosynthetic pathway to paclitaxel analogues, we repurposed the adenylation and thiolation domains (Phe-AT) of a nonribosomal peptide synthetase (TycA) so that they would function as a CoA ligase. Twenty-eight isoserine analogue racemates were synthesized by an established procedure based on the Staudinger [2+2] cycloaddition reaction. Phe-AT converted 16 substituted phenylisoserines, one β-(heteroaryl)isoserine, and one β-(cyclohexyl)isoserine to their corresponding isoserinyl CoAs. We imagine that these CoA thioesters can likely serve as linchpin biosynthetic acyl donors transferred by a 13-O-acyltransferase to a paclitaxel precursor baccatin III to make drug analogues with better efficacy. It was also interesting to find that an active site mutant [Phe-AT (W227S)] turned over 2-pyridylisoserine and the sterically demanding p-methoxyphenylisoserine substrates to their CoA thioesters, while Phe-AT did not. This mutant is promising for further development to make 3-fluoro-2-pyridylisoserinyl CoA, a biosynthetic precursor of the oral pharmaceutical tesetaxel used for gastric cancers.

Recent advances in the study of the bioactive conformation of taxol

Paclitaxel is one of the most important chemotherapeutic drugs in the fight against cancer. This minireview covers the recent advances in the study of the bioactive conformation of paclitaxel in tubulin/microtubules. The tubulin-bound structure of paclitaxel has been studied by means of photoaffinity labeling, cryo-electron microscopy, solid-state NMR, molecular modeling, MD simulations and the synthesis of conformationally restrained analogues and paclitaxel mimics. The bioactive conformation of paclitaxel is important since it could provide critical information that would allow the design of novel analogues with simpler structures and/or increased potency against cancer.

Promotion of tubulin assembly by poorly soluble taxol analogs

Promotion or inhibition of tubulin assembly into microtubules is the standard in vitro assay for evaluating potential antimicrotubule agents. Many agents to be tested are poorly soluble in aqueous solution and require a cosolvent such as dimethyl sulfoxide (DMSO). However, DMSO itself can promote tubulin assembly, and its inclusion in assays for compounds that induce tubulin assembly complicates interpretation of the results. Substituting GDP for GTP in the exchangeable nucleotide binding site of tubulin produces a less active form of the protein, tubulin-GDP. Here it is shown that tubulin-GDP can be assembled into normal microtubules in DMSO concentrations up to 15% (v/v), and polymerization assays performed under these conditions can be compared with assays run under more standard conditions. Assays for measuring the effective concentration of a ligand for promotion of tubulin assembly (EC(50)), measuring the concentration for inhibition of tubulin assembly (IC(50)) by a colchicine site ligand, and measuring tubulin critical concentrations in the presence of poorly soluble taxol derivatives are illustrated.