For the progress of the in vivo study on sulphostin, a dipeptidyl peptidase IV inhibitor, its large-scale synthetic method was investigated. The optical resolution of (3 S, RS P)-1-amino (sulfoamino) phosphinyl-3-benzyloxycarbonylamino-2-piperidin-one, which was the most difficult step in the previous method, was simplified by using fractional crystallization. The use of 2 mol equiv of (1 S, 2 R)-(+)-2-amino-1, 2-diphenylethanol for optical resolution ...