A novel gastroprotective substance, 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)-ammoniohexanoate (AI-77-B, 1), isolated from a culture broth of Bacillus pumilus AI-77, was chemically modified to prodrugs that are active by oral dosing. Compound 1 was lactonized and then monoalkylated at the primary amine position. Six N-alkylated gamma-lactone derivatives of 1 (with alkyl chains being methyl 5a, ethyl 5b, n-propyl 5c, n-butyl 5d, n-pentyl 5e, or n-hexyl 5f) were synthesized and eight compounds including 1 and gamma-lactone derivative 2 were compared for their gastroprotective activities and blood levels after oral administration in rats. Further, chloroform-water partition coefficients of 5a-f were also compared as a measure of lipid solubility. The protective effects of these compounds on stress ulcers were mutually related to blood levels of dealkylated compounds (1 and 2). Parent compound 1 was detected in blood at 1 h after each of 5a-d was administered. When 5b or 5c was administered, high activity and high blood levels of 1 were observed in comparison with those levels obtained with 5a or 5d. Neither 5e nor 5f were detected in any amount in blood by oral administration without special formulation due to extremely low solubilities and agglutinative properties in intestinal fluid. Interestingly, 5b and 5c were found to have antiinflammatory activities in addition to potent antiulcerogenicity action.