[GRAPHICS]An enantioselective total synthesis of Al-77-B (1), a gastroprotective substance isolated from a culture broth of Bacillus pumilus Al- 77, was performed in high overall yield. In this synthesis, the dihydroisocoumarin part 14 and the dihydroxyamino acid part 20 were both assembled from D-ribose as the common chiral source, For the construction of 14 a bromobenzofuran derivative was used as a novel salicylic acid synthon. Finally, DEPC-mediated condensation of 14 and 20 yielded Al-77-B (1).
A short totalsynthesis of AI-77-B (1) is reported, which produces the natural enantiomer using S-leucine and S-aspartic acid as the optically active starting materials.
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
The structures and the chemicalnature of a novel gastroprotective substance AI-77-B (1) and its analogues AI-77-C (2), D (3), F (4) and G (5), which are produced by Bacillus pumilus AI-77, are described. The structure of 1 was confirmed to be 6-[[1(S)-(3(S), 4-dihydro-8-hydroxy-1-oxo-1H-2-benzopyran-3-yl)-3-methylbutyl]amino]-4(S),5(S)-dihydroxy-6-oxo-3(S)-aminohexanoic acid by X-ray in combination