First totalsynthesis of AI-77-B (1), a gastroprotectivesubstance from Bacillus pumilus AI-77, was achieved in a stereoselective and convergent manner. In this synthesis, the dihydroisocoumarin part 2 was constructed in one step through 1,2-addition of the benzylic anion 17b to Boc-L-leucinal 7b. The hydroxy amino acid 4 was elaborated from (R)-glutamic acid in a highly stereoselective manner. Condensation
and inhibition tests of new low molecular weight thrombin inhibitors utilizing cyanopeptides, the secondary metabolites of cyanobacteria with interesting biological activities, as new lead structures. Starting with aeruginosin 98‐B (1) as a lead structure, we have developed and synthesised new, selective acting inhibitors of serineproteases (RA‐1005 and RA‐1009, which are suitable targets for further