The organic extract of the sea hare Aplysia kurodai collected in Mie Prefecture, which showed remarkable cytotoxicity, was subjected to bioassay-guided fractionation by repeated chromatography, resulting in the isolation of an active component named aplyronine (1). Aplyronine (1) was found to exhibit the potent in vivo antitumor activities against various murine tumors. The gross structure of 1 was deduced by means of 2D NMR spectroscopy (^1H-^1H and ^<13>C-^1H COSY, HMBC) and was confirmed on the basis of the detailed NMR spectral analysis of two amino acid derivatives (5 and 6) and four fragments (8a, 8b, 9, and 10) obtained by chemical degradation of 1. As part of a study on the absolute stereostructure of aplyronine (1), an enantioselective synthesis of the fragment 10 was carried out, disclosing the absolute stereochemistry of eight chiral centers (C23-C26 and C29-C32) in 1 as shown in 10c.
