Stereochemistry of the methyl group in (R)-3-methylitaconate derived by rearrangement of 2-methylideneglutarate catalysed by a coenzyme B-12-dependent mutase
D. Ciceri et al., Stereochemistry of the methyl group in (R)-3-methylitaconate derived by rearrangement of 2-methylideneglutarate catalysed by a coenzyme B-12-dependent mutase, HELV CHIM A, 83(9), 2000, pp. 2550-2561
2-Methylidenegtutarate mutase is an adenosylcobalamin (coenzyme B-12)-depen
dent enzyme that catalyses the equilibration of 2-methylideneglutarate with
(R)-3-methylitaconate. This reaction is believed to occur via protein-boun
d free radicals derived from substrate and product. The stereochemistry of
the formation Of the methyl group of 3-mechylitaconate has been probed usin
g a 'chiral methyl group'. The methyl group in 3-([H-2(1),H-3]methyl)itacon
ate derived from either (R)- or (S)-2-methylidene[3-H-2(1),3-H-3(1)]glutara
te was a 50:50 mixture of (R)- and (S)-forms. It is concluded that the barr
ier to rotation about the C-C bond between the methylene radical centre and
adjacent C-atom in the product-related radical [(CH)-C-.,CH(-O2CC=CH2)CO2-
] is relatively low, and that the interaction of the radical with cob(II)al
amin is minimal. Hence, cob(II)alamin is a spectator of the molecular rearr
angement of the substrate radical to product radical.