Abstract: A novel benzothiazole or benzimidazole derivative represented by formula (I) ##STR1## wherein X represents a sulfur atom or a NH group; R.sup.1 represents a hydrogen atom, a lower alkoxy group, a chlorine atom, a bromine atom or an iodine atom; R.sup.2 represents a hydrogen atom a substituted or unsubstituted lower alkyl group, a vinyl group, an aryl group or an acyl group; m is an integer of 1, 2 or 3; and n is an integer of 0, 1 or 2, which shows an excellent acid secretion suppressing effect and gastric mucosa protecting effect, and an antiulcer agent containing the same as an active ingredient.

Abstract: A therapeutic and/or prophylactic agent for viral infection, particularly human immunodeficiency virus (HIV) infection, which comprises as an active ingredient a lactam compound represented by formula (I) ##STR1## wherein X represents --COOR, wherein R represents a hydrogen atom or a straight-chain or branched-chain alkyl group having from 1 to 8 carbon atoms, or ##STR2## wherein n represents an integer of 2 or 3 and A represents methine when n is 2 or a quarternary carbon atom when n is 3, or a pharmaceutically acceptable salt or ester derivative thereof.

Abstract: As new compounds are provided a class of derivatives of actinonin represented by the general formula ##STR1## where R is a hydrogen or a lower alkyl group, which can exhibit the enzyme-inhibitory activities to a limited range of peptidases and show a remarkable enzyme-specificity, and which are effective to treat a cycloheximide-induced experimental amnesia in mice and are expectable to be useful to treat an amnesia in a mammalian animal, including human.