The first totalsynthesis of (+)-crassalactone B (2) and a new syntheses of (+)-crassalactone C (3) has been achieved starting from d-glucose. The natural products 2 and 3 can be selectively accessed by changing the conditions for TBDPS cleavage in the final intermediate 16. The synthesized natural products were evaluated for their cytotoxic activity against a panel of human tumour cell lines.
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