Provided are excellent .beta.-secretase inhibitors, that is, compounds represented by the general formula (1) or prodrugs thereof: ##STR00001## wherein A is amino or protected amino; B.sup.1 and B.sup.2 are each a single bond, alkylene of 1 to 3 carbon atoms, or the like; D is a single bond, --NHCO, or the like; E is --COOH, tetrazole ring, or the like; n is an integer of 1 to 3; m is an integer of 1 to 3; G is hydroxyl, a group represented by the general formula (2), or the like: ##STR00002## in which Z is --NH, -Asp-Ala-NH--, -Asp-Ala-, -Asp-NH--, or the like; L is a 5-to 10-membered ring optionally containing a heteroatom and/or unsaturated bond; X is --COOH, tetrazole ring, or the like; Y is hydrogen, --COOH, or the like; and k is an integer of 1 to 4; and R.sup.1, R.sup.2, and R.sup.3 are each alkyl of 1 to 6 carbon atoms, or the like.