Concise synthesis of AHMHA unit in perthamide C. Structural and stereochemical revision of perthamide C

Diastereomers of 3-amino-2-hydroxy-6-methylheptanoic acid (AHMHA), a new amino acid unit in perthamides C and D, have been synthesized from commercially available 4-methylpentanol in a concise manner and 50% average overall yield. Comparison of the H-1 and C-13 NMR data, optical rotation data and Marfey's analysis of the resulting isomers with the natural fragment unambiguously allowed the configurational assignment of the natural residue as (2R,3R). A structural revision of perthamides C and D is also reported. (C) 2010 Elsevier Ltd. All rights reserved.