title: Synthesis and crystal structures of Boc-L-Asn-L-Pro-OBzl.CH3OH and dehydration side product, Boc-beta-cyano-L-alanine-L-Pro-OBzl.
abstract: Boc-L-Asn-L-Pro-OBzl: C21H29O6N3.CH3OH, Mr = 419.48 + CH3 OH, monoclinic, P2(1), a = 10.049(1), b = 10.399(2), c = 11.702(1) A, beta = 92.50(1)degrees, V = 1221.7(3) A3, dx = 1.14 g.cm-3, Z = 2, CuK alpha (lambda = 1.54178 A), F(000) = 484 (with solvent), 23 degrees, unique reflections (I greater than 3 sigma(I)) = 1745, R = 0.043, Rw = 0.062, S = 1.66. Boc-beta-cyano-L-alanine-L-Pro-OBzl: C21H27O5N3, Mr = 401.46, orthorhombic, P2(1)2(1)2(1), a = 15.741(3), b = 21.060(3), c = 6.496(3) A, V = 2153(1) A3, dx = 1.24 g.cm-3, Z = 4, CuK alpha (lambda = 1.54178 A), F(000) = 856, 23 degrees, unique reflections (I greater than 3 sigma(I)) = 1573, R = 0.055, Rw = 0.078, S = 1.86. The tert.-butyloxycarbonyl (Boc) protected dipeptide benzyl ester (OBzl), Boc-L-Asn-L-Pro-OBzl, prepared from a mixed anhydride reaction using isobutylchloroformate, Boc-L-asparagine, and HCl.L-proline-OBzl, crystallized with one methanol per asymmetric unit in an extended conformation with the Asn-Pro peptide bond trans. Intermolecular hydrogen bonding occurs between the methanol and the Asn side chain and between the peptide backbone and the Asn side chain. A minor impurity due to the dehydration of the Asn side chain to a beta-CNala crystallized with a similar extended conformation and a single intermolecular hydrogen bond.
authors.affiliation: Department of Biochemistry, Howard Hughes Medical Institute, Dallas, Texas.
authors.forename: A N
authors.initials: AN
authors.lastname: Stroup
authors.forename: L B
authors.initials: LB
authors.lastname: Cole
authors.forename: M M
authors.initials: MM
authors.lastname: Dhingra
authors.forename: L M
authors.initials: LM
authors.lastname: Gierasch
mesh_terms: D000595:Amino Acid Sequence; D004151:Dipeptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011392:Proline / Q000737:chemistry; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D004151:Dipeptides; C068660:t-butyloxycarbonyl-cyanoalanylproline benzyl ester; C068659:t-butyloxycarbonyl-asparaginylproline benzyl ester; D011392:Proline