It was found that lithium aluminum hydride reduction of Na, NG-disubstituted arginine lactam (3a-c) at a low temperature gave a corresponding argininal derivative (4a-c). Analogous reduction of acetyl-L-leucyl-L-leucyl-N-benzyloxycarbonyl-L-arginine lactam (8b) or its dipeptide analog (13) yielded leupeptin Ac-LL (1a) or acetylleucylargininal (11) respectively. Antiplasmin activities of these synthetic leupeptins were also reported.