Cis Effects in the Cobalt Corrins. 1. Crystal Structures of 10-Chloroaquacobalamin Perchlorate, 10-Chlorocyanocobalamin, and 10-Chloromethylcobalamin.

The crystal structures of 10-chloroaquacobalamin perchlorate hydrate (10-Cl-H(2)OCbl.ClO(4)) (Mo Kalpha, 0.710 73 Å, monoclinic system, P2(1), a = 11.

Side Chain Entropy and the Activation of Organocobalamins for Carbon-Cobalt Bond Homolysis: Synthesis, Characterization, and Thermolysis of the Neopentyl Derivative of a Unique Cobalamin Analog Lacking a c Side Chain.

Hydrodeamination of the c-amino derivative, 5, of cyanocobalamin (CNCbl) with hydroxylamine-O-sulfonic acid in aqueous base leads to an extensively rearranged product instead of the c side chain truncated derivative, 1, expected from simple deamination. The rearranged product (CNCbl-8-butanamide) crystallizes in the orthorhombic system, space group P2(1)2(1)2(1) with unit cell dimensions a = 16.041(11), b = 21.

Diastereomeric Control in the Formation of Carbon-Cobalt Bonds in Organocobalt Corrinoids: Reactions of Cobalt(II) Corrinoids with Organic Hydroperoxides(1).

1,1-Dimethylpropyl hydroperoxide reacts with cobalt(II) cobinamide via a Fenton-like reaction to produce a mixture of the diastereomeric alpha- and beta-ethylcobinamides (CH(3)CH(2)Cbi(+)'s, in which the organic ligand is in the "lower" or "upper" axial ligand position, respectively), the composition of which depends on the ratio of starting materials. When the hydroperoxide reagent is in excess, <2% of the CH(3)CH(2)Cbi(+) product is the alpha diastereomer, a product distribution which agrees with previous observations of the equilibrium mixture. This distribution apparently arises because the previously demonstrated CH(3)CH(2)(*)-promoted isomerization of CH(3)CH(2)Cbi(+) diastereomers leads to equilibration.

Thermolysis of Neopentylcobalamin Analogs Complexed to Haptocorrin: Side Chain Entropy and Activation of Organocobalamins for Carbon-Cobalt Bond Homolysis.

The kinetics of the thermal Co-C bond homolysis of the complexes of a vitamin B(12) binding protein (haptocorrin) with a series of analogs of neopentylcobalamin modified in side chain structure have been studied. The analogs include the C13 epimer in which the e propionamide side chain adopts an "upwardly" axial conformation and a series of c side chain-modified analogs, including the c-monocarboxylate, the c-N-methylamide, the c-N,N-dimethylamide, and the c-N-isopropylamide. Activation parameters for the thermal homolysis of these complexes show that the previously observed stabilization of alkylcobalamins by haptocorrin is due to both enthalpic and entropic factors.