Reaction catalyzed by pepsin A (3.4.23.1)

		+			=		tert-butyl (3S)-3-[(R)-hydroxy(4-nitrophenyl)methyl]-4-oxopiperidine-1-carboxylate
	4-nitrobenzaldehyde	+		tert-butyl 4-oxopiperidine-1-carboxylate	=		tert-butyl (3S)-3-[(R)-hydroxy(4-nitrophenyl)methyl]-4-oxopiperidine-1-carboxylate