The 15N NMR spectra of a series of derivatives of 2‐amino‐2‐deoxy‐β‐D‐glucopyranose and dipeptides or secondary amines were recorded. In the dipeptide derivatives the chemical shift of nitrogen atom N‐1 (linked to sugar) is essentially unchanged and the shifts of nitrogen atoms N‐3 and N‐6 are determined by the nature of the R1 and R2 substituents at C‐α carbon of the amino acid unit. The highest shielding
Photoaffinity reagents for pepsin [Ala–Gly–Phe(N3), Gly–Gly–Phe(N3)–Phe–Gly–OEt, Gly–Gly–Phe–Phe(N3)–Gly–OEt] were synthesized by a solution method. The pentapeptides were cleaved rapidly at the peptide bond between two aromatic amino acid residues by pepsin. This shows that Phe(N3) residues of the photoaffinity reagents bind with the S1 or S1′ site of pepsin. Pepsin was irradiated with photoaffinity reagents and the remaining activity was measured. The pepsin activity was decreased more rapidly in the presence of photoaffinity reagents, compared with that in the absence of photoaffinity reagents. Photoaffinity labeling occured at pH 2.0; however, did not occur at pH 4.0. Photoaffinity labeling of pepsin with 3H-labeled Gly–Gly–Phe(N3)–Phe–Gly–OEt showed that about 9% of the pepsin bound covalently with the photoaffinity reagent.