Diversity-Oriented Asymmetric Synthesis of Hapalosin: Construction of Three Small C9/C4/C3-Modified Hapalosin Analogue Libraries

A flexible approach to the β-hydroxy γ-amino acid residue (fragment C) of hapalosin has been developed on the basis of the the regio- and diastereoselective Grignard reaction. The method allows the introduction of different side chains at the C9 of hapalosin. Asymmetric syntheses of hapalosin (1a), 9-homohapalosin (1b), 9-i-butyl-hapalosin (1c), 8-epi-hapalosin (epi-1a), and three small libraries diversified at C9 (3-member, 1L3), C9/ C4 (9-member, 1L9), or C9/C4/C3 (27-member, 1L27) have been produced using this method.