title: Transesterification of Moz-Asn-Leu-Gly-OEt in methanol. Confirmation of Ca2+ mediated catalysis.
abstract: During the recrystallization of the crude protected tripeptide ester Moz-Asn-Leu-Gly-OEt (obtained by an enzymatic coupling reaction) in methanol/water, the transesterification of this compound to methyl ester was observed. The involvement of Ca2+ in this process was indicated by the results obtained in the following experiments: 1) incubation of crude Moz-Asn-Leu-Gly-OEt in methanol solutions of o-phenanthroline and EDTA; 2) recrystallization of the crude Moz-Asn-Leu-Gly-OEt in ethanol/water followed by incubation in methanol; 3) determination of the Ca2+ content of the crude Moz-Asn-Leu-Gly-OEt. After recrystallization Moz-Asn-Leu-Gly-OEt lost the ability to be transesterified in methanol. However, in the presence of crude Moz-Asn-Leu-Gly-OEt, or calcium acetate, or a mixture of calcium chloride/sodium acetate, the compound was transesterified, suggesting that the transesterification of crude and recrystallized compounds occurs through different mechanisms. On the basis of these results, and of the conformational data obtained for these peptides by 1H-NMR, we suggest models for the transesterification reactions.
authors.affiliation: Department of Biochemistry, University of São Paulo, Brazil.
authors.forename: M T
authors.initials: MT
authors.lastname: Miranda
authors.forename: H
authors.initials: H
authors.lastname: Morita
authors.forename: M
authors.initials: M
authors.lastname: Tominaga
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D002384:Catalysis; D003460:Crystallization; D004492:Edetic Acid / Q000494:pharmacology; D004951:Esterification; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D000432:Methanol; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry* / Q000378:metabolism; D010618:Phenanthrolines / Q000494:pharmacology; D012996:Solutions
chemical_list: D009842:Oligopeptides; D010618:Phenanthrolines; D012996:Solutions; C070751:4-methoxybenzyloxycarbonyl-asparaginyl-leucyl-glycine ethyl ester; D004492:Edetic Acid; D002118:Calcium; C025205:1,10-phenanthroline; D000432:Methanol