Synthesis of the polyketide section of seragamide A and related cyclodepsipeptides via Negishi cross coupling.

The synthesis of the polyketide section present in the potently cytotoxic marine cyclodepsipeptide jasplakinolide and related natural products, geodiamolides and seragamides, is reported. The key step is a Negishi cross coupling of ()-(3-methoxy-2-methyl-3-oxopropyl)zinc(II) bromide and an ()-iodoalkene that was synthesized via an aluminium ester enolate attack at ()-propylene oxide. The overall synthesis comprises nine steps with an overall yield of 21%.

Total Synthesis of the Marine Natural Product Hemiasterlin by Organocatalyzed α-Hydrazination.

An efficient synthesis of the potently cytotoxic marine peptide hemiasterlin is presented. The tetramethyltryptophan moiety is assembled by tert-prenylation of indole, followed by the high-yielding organocatalyzed α-hydrazination of a sterically congested aldehyde with excellent enantioselectivity. 2-Bromo-N-ethylpyridinium tetrafluoroborate (BEP)-mediated peptide coupling completes the synthesis, being the first approach that does not employ chiral auxiliaries.