Reaction catalyzed by pepsin A (3.4.23.1)

		+			=		(3R,4S)-3-(benzyloxy)-4-hydroxy-4-(4-nitrophenyl)butan-2-one
	4-nitrobenzaldehyde	+		1-(benzyloxy)propan-2-one	=		(3R,4S)-3-(benzyloxy)-4-hydroxy-4-(4-nitrophenyl)butan-2-one