Stereoselective synthesis of (2R,3R,4R)-3-hydroxy-2,4,6-trimethylheptanoic acid and determination of the absolute stereochemistry of the natural product from Callipeltin A

A revised stereostructure of 3-hydroxy-2,4,6-trimethylheptanoic acid, the beta-hydroxy acid that acylates the N-terminus of callipeltin A. is proposed on the basis of analysis of J-coupling in the H-1 NMR spectrum of the acetonide derivative obtained front the acid hydrolysate of callipeltin A. The proposed structure was definitively confirmed by enantioselective synthesis.