Reaction catalyzed by pepsin A (3.4.23.1)

		+			=		(3S)-3-[(R)-hydroxy(4-nitrophenyl)methyl]oxan-4-one
	4-nitrobenzaldehyde	+		oxan-4-one	=		(3S)-3-[(R)-hydroxy(4-nitrophenyl)methyl]oxan-4-one