Total Synthesis of the Gastroprotective Substance AI‐77‐B and of Analogues

The Diels ‐ Alder adducts 8 of furan to 1‐cyanovinyl acetate were converted into (Methyl 3‐chloro)‐5‐ O ‐(3‐chlorobenzoyl)‐2, 3‐dideoxy‐α‐dl‐arabino‐hexofuranosid)uronic acid ((α)‐ 18a ) and into (methyl 3‐azido‐5‐ O ‐(3‐chlorobenzoyl_‐2,3‐dideoxy‐α‐dl‐ribo‐hexofuranosid)uronic acid ((α)‐ 41a ). These compounds were condensed to (3 S )‐3‐[(1′ S )‐1′‐amino‐3′‐methylbutyl]‐3,4‐dihydro‐8‐hydroxyisocoumarin hydrochloride ((−)‐ 2 ); the resulting mixtures of diastereoisomeric amides were transformed and separated to give the gastroprotective substance AI‐77‐ B ((−)‐ 1 ) and analogues.