title: Regioselective synthesis and electron impact mass spectral fragmentation differentiation of 2- or 3-isopropylthio, phenylthiosuccinic acid 4-methyl/isopropyl ethers.
abstract: 2- and 3-isopropylthio/phenylthiosuccinic acid 4-methyl/isopropyl esters were synthesized regioselectively by Michael additions of isopropylthiol/thiophenol to maleic anhydride, followed by alcoholysis with methanol/isopropanol. Their mass spectrometric behavior has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate an alkoxy group, an alcohol, or an alkoxycarbonyl group from the respective molecular ion. Some molecular ions also show a tendency to eliminate a molecule of water, propene or CO(2). The [M - MeCH = CH(2)](+) ions could further lose H(2)O to form substituted succinic anhydride ions, or lose CO(2) to form 3-substituted propionic acid ions. Both of these ions could further yield other small fragment ions by loss of CO(2)H, CO or other small fragments. It has been found that 2-isopropylthio- and 3-phenylthiosuccinic acid 4-esters show more abundant [M - H(2)O](+) peaks than their 3-isopropylthio and 2-phenylthio isomers in their mass spectra.
authors.affiliation: College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
authors.forename: J
authors.initials: J
authors.lastname: Xu
authors.forename: D
authors.initials: D
authors.lastname: Wang
authors.forename: Q
authors.initials: Q
authors.lastname: Zhang
authors.forename: A
authors.initials: A
authors.lastname: Huang
mesh_terms: D002268:Carboxypeptidases / Q000037:antagonists & inhibitors; D043422:Carboxypeptidases A; D013058:Mass Spectrometry; D018716:Molecular Mimicry; D010455:Peptides / Q000737:chemistry; D011480:Protease Inhibitors / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism; D013386:Succinates / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D010455:Peptides; D011480:Protease Inhibitors; D013386:Succinates; D002268:Carboxypeptidases; D043422:Carboxypeptidases A