A simple and efficient stereoselective synthesis of (−)-cleistenolide

Synthesis and antimicrobial activity of (-)-cleistenolide and analogues

Using the "chiral pool" approach, two modified total syntheses of the biologically active δ-lactone cleistenolide (1) have been achieved starting from d-glucose. These approaches also enabled the preparation of novel analogues and derivatives of natural product 1. The applied strategy for the synthesis of 1 involves: the initial degradation of the chiral precursor for a single C-atom, C₂-fragment chain extension using Z-selective Wittig reaction, and the final δ-lactonization. All tested cleistenolide analogues displayed antimicrobial activity against a panel of nine microbial strains, most of them superseding the activity of cleistenolide itself, and, in some cases, coming close in value to the observed minimal inhibitory concentrations of chloramphenicol. Increased lipophilicity of the derivatives and the non-sterically congested conjugated lactone moiety were a prerequisite for analogues with high inhibitory activity against S. aureus and, in general, Gram-positive bacteria.

Synthesis, antiproliferative activity and SAR analysis of (-)-cleistenolide and analogues

A new, modified total synthesis of (-)-cleistenolide (1) and sixteen new analogues or derivatives was achieved starting from commercially available 1,2-O-isopropylidene-α-d-glucofuranose. The synthesis of 1 proceeds in six steps and 67% overall yield, using single-carbon atom degradation of a protected chiral precursor, (Z)-selective Wittig olefination, and acid catalyzed δ-lactonization. A new Lewis acid promoted procedure for one-pot O-debenzylation/O-acylation has been developed to complete the synthesis of natural product 1 and selected analogues. The synthesized compounds were tested in vitro to evaluate their cytotoxicity against K562, HL-60, Jurkat, Raji, MCF-7, MDA-MB 231, HeLa, A549, and MRC-5 cell lines. All (-)-cleistenolide analogues exhibited significantly higher cytotoxicity than lead 1 against the majority of cell lines tested. Most of the synthesized compounds are more active than doxorubicin on at least one malignant cell line, but were almost completely inactive against normal MRC-5 cells. The structural features of the tested compounds responsible for their antiproliferative activity have been identified by preliminary SAR analysis.