Stereoselective synthesis of protected (2R,3R,4S)-4,7-diamino-2,3- dihydroxyheptanoic acid: A novel amino acid of callipeltins A and D

An orthogonally protected derivative 1 of (2R,3R,4S)-4,7-diamino-2,3- dihydroxyheptanoic acid, the unusual amino acid residue of the biologically active marine peptides such as callipeltins A and D and neamphamide A, was efficiently prepared in 10 steps and 30% overall yield from a commercially available L-ornithine derivative 2. The key step includes the N-diphenylmethylene-controlled diastereoselective dihydroxylation of (Z)-ester 3 with > 13:1 selectivity for the desired isomer.