Approaches to isozyme-specific inhibitors. 16. A novel methyl-C5' covalent adduct of L-ethionine and beta,gamma-imido-ATP as a potent multisubstrate inhibitor of rat methionine adenosyltransferases.
N6,N6-Dibenzoyl-2',3'-O-isopropylideneadenosine, which is readily synthesized by one-pot 5'-O-trimethylsilylation, N6-benzoylation, and desilylation, was converted to the corresponding 5'-aldehyde. This was treated with CH2 = CHMgBr to afford, after debenzoylation, a 1:3 mixture of the 5'S and 5'R epimers, respectively, of 5'-C-vinyl-2',3'-O-isopropylideneadenosine. The configurations were established by single-crystal X-ray diffraction analysis of the 5'R epimer. Hydroboration of the 5'-O-tetrahydropyranyl derivative of the mixed epimeric 5'-C-vinyl nucleosides readily furnished 5'(S,R)-C-(2-hydroxyethyl)-2',3'-O-isopropylideneadenosine. Treatment of the 5'(S,R)-C-(2-O-tosyl) derivative of this with disodium L-homocysteinate permitted facile introduction of the L-ethionine system. By means of methods developed earlier in the synthesis of homologous methionine-ATP adducts, the alpha-amino acid group was protected, a beta,gamma-imidotriphosphoryl group was introduced at O5', and blocking groups were removed to give the title adduct as a 2:3 mixture of its two 5' epimers. It was a powerful inhibitor [KM(ATP)/Ki = 520 and 340] of the M-2 (normal tissue) and M-T (hepatoma tissue) forms, respectively, of the title enzyme and displayed predominantly competitive kinetics with the two substrates L-methionine and MgATP. It inhibited M-2 and M-T slightly less effectively than its homologue possessing one less CH2 between sulfur and C5' and gave kinetic evidence of an increased tendency to form L-methionine-enzyme-adduct and MgATP-enzyme-adduct complexes.
Vrudhula
V M
VM
Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111.
Kappler
F
F
Afshar
C
C
Ginell
S L
SL
Lessinger
L
L
Hampton
A
A
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000266:Adenylyl Imidodiphosphate / Q000138:chemical synthesis / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive; D055598:Chemical Phenomena; D002621:Chemistry; D002851:Chromatography, High Pressure Liquid; D005001:Ethionine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008715:Methionine / Q000378:metabolism; D008716:Methionine Adenosyltransferase / Q000037:antagonists & inhibitors*; D015394:Molecular Structure; D051381:Rats; D013329:Structure-Activity Relationship; D014166:Transferases / Q000037:antagonists & inhibitors*
D007527:Isoenzymes; D000266:Adenylyl Imidodiphosphate; D000255:Adenosine Triphosphate; D008715:Methionine; D014166:Transferases; D008716:Methionine Adenosyltransferase; D005001:Ethionine