Isozyme-specific enzyme inhibitors. II. L-homocysteine-ATP S-C5′ covalent adducts as inhibitors of rat methionine adenosyltransferases

Francis Kappler, Ton T. Hai, Robert J. Cotter, Robert J. Cotter, Alexander Hampton

Research output: Contribution to journalArticle

Abstract

The title compounds (14a,b) were 5′ epimers of a derivative of a phosphonate isostere of ATP in which the CH2OPα system of ATP was replaced by CH(R)CH2Pα [R = L-S(CH2)2CH(NH2)CO2H]. They resisted synthesis via attempted S-alkylation of the corresponding epimeric 5′-mercapto derivatives. A practicable route to 14a,b commenced with Michael condensation of L-homocysteine with the diphenyl ester of the 5′,6′-vinyl phosphonate analogue of 2′,3′-O-isopropylideneadenosine 5′-phosphate. The resulting epimeric 5′ thioethers were separated by reverse-phase HPLC. The two phenyl groups were replaced by benzyl groups, after which the α-amino acid residue was protected as an N-Boc methyl ester. Both benzyl groups were removed by hydrogenolysis, and the resulting phosphonic acid was converted into its pyrophosphoryl derivative. Blocking groups were then removed under conditions that furnished 14a and 14b without racemization of their L-amino acid residues. Also synthesized were the Pβ-NH-Pγ imido analogue (15a) of 14a and the sulfoxide derivative (16a) of 14a. The structures of 14a and 16a were verified by FAB mass spectra, which revealed the protonated molecular ions of their sodium salts. All adducts appeared to function as dual substrate site inhibitors (competitive to ATP and to methionine) of the rat normal tissue (MAT-2) form of methionine adenosyltransferase (MAT); 14a and 15a [KM(ATP)/Ki = 4 and 9, respectively] were the most effective. Adduct 15a was the most effective inhibitor [KM(ATP)/Ki = 13] of the MAT-T form from rat hepatoma tissue; the kinetic data indicated dual-site inhibition by 15a with apparently complete coverage of the ATP site and incomplete coverage of the methionine site. The inhibition properties of the adducts indicated little preference in the order in which the two MAT forms bound ATP and methionine.

Original languageEnglish (US)
Pages (from-to)1030-1038
Number of pages9
JournalJournal of Medicinal Chemistry
Volume29
Issue number6
StatePublished - 1986

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Methionine Adenosyltransferase
Homocysteine
Enzyme Inhibitors
Isoenzymes
Rats
Adenosine Triphosphate
Methionine
Derivatives
Organophosphonates
sulfoxide
Esters
Tissue
Amino Acids
Hydrogenolysis
Alkylation
Sulfides
Condensation
Hepatocellular Carcinoma
Salts
Sodium

ASJC Scopus subject areas

  • Organic Chemistry

Cite this

Isozyme-specific enzyme inhibitors. II. L-homocysteine-ATP S-C5′ covalent adducts as inhibitors of rat methionine adenosyltransferases. / Kappler, Francis; Hai, Ton T.; Cotter, Robert J.; Cotter, Robert J.; Hampton, Alexander.

In: Journal of Medicinal Chemistry, Vol. 29, No. 6, 1986, p. 1030-1038.

Research output: Contribution to journalArticle

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