Enhancing the methyl-donor activity of methylcobalamin by covalent attachment of DNA.
The preparation of a covalent DNA conjugate of vitamin B12 by means of heterogeneous solid-phase synthesis is reported. The cyano-corrinoid made available, dipotassium Co(beta)-cyanocobalamin-(3''-->2'),(3''-->5')-bis-2''-deoxythymidyl-3''-ate (K(2)-4), was cleanly methylated at the Co center by electrosynthetic means. Aqueous solutions of the resulting organometallic DNA-B12 conjugate K(2)-5 exhibited spectroscopic properties indicative of significant weakening of the axial (Co-N) bond, together with a 25-times higher basicity relative to Co(beta)-methylcobalamin (2). Methyl-transfer equilibria of pH-neutral aqueous solutions of K(2)-5 and cob(I)alamin (K-7) on one side, and of cob(I)alamin-(3''-->2'),(3''-->5')-bis-2''-deoxythymidyl-3''-ate (K(3)-8) and methylcobalamin (2) on the other, were studied at room temperature (Scheme 3). The NMR-derived data provided an equilibrium constant of ca. 0.3. Activation of K(2)-5 for abstraction of its Co-bound Me group by a nucleophile (such as cob(I)alamin) was, thus, indicated.
Fasching
Mario
M
Institute of Organic Chemistry, University of Innsbruck, Innrain 52a, A-6020 Innsbruck.
Perschinka
Hannes
H
Eichmüller
Christian
C
Gschösser
Sigrid
S
Kräutler
Bernhard
B
D004247:DNA / Q000737:chemistry*; D008745:Methylation; D015394:Molecular Structure; D014805:Vitamin B 12 / Q000031:analogs & derivatives* / Q000737:chemistry
D004247:DNA; C019476:mecobalamin; D014805:Vitamin B 12