The Diels-Alder adducts 8 of furan to 1-cyanovinyl acetate were converted into (methyl 3-chloro-5-043-chlorobenzoyl)-2,3-dideoxy-alpha-DL-arabino-hexofuranosid )uronic acid ((+/-)-18a) and into (methyl 3-azido-5-0-(3-chlorobenzoyl)-2,3-dideoxy-alpha-DL-ribo-hexofuranosid)ur onic acid ((+/-)-41a). These compounds were condensed to (3S)-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.