Divergent total synthesis of crassalactones B and C and evaluation of their antiproliferative activity

Abstract

A divergent total synthesis of cytotoxic natural products (+)-crassalactones B (2) and C (3) has been achieved by utilizing diacetone d-glucose (4) as a chiral precursor. The key steps of the synthesis of both targets 2 and 3 were a stereo-selective addition of phenyl magnesium bromide to a dialdose derivative, a regioselective introduction of the cinnamic acid residue, and a stereospecific furano-lactone ring formation by cyclocondensation of a suitable hemiacetal derivative with Meldrum's acid. No protection is necessary for the synthesis of the (+)-crassalactone C (3), except the diacetonide function that is already present in the commercially available starting material 4. Preparation of (+)-crassalactone B (2) from the same starting material, requires the use of a single silyl ether protecting group throughout the synthesis. The synthesized natural products were evaluated for their in vitro antiproliferative activity against PC3, HT29 and A549 human tumour cell lines.