[Back]

B. Kräutler, C. Caderas, R. Konrat, M. Puchberger, C. Kratky:
"Lipophilic Functionalized Cobyrinic-Acid Derivatives. Part 1. Cobester α-monoacids (α,α,α,β,β,β-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates)";
Helvetica Chimica Acta, 78 (2004), 3; 581 - 599.

The four α,α,α,β,β,β-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates 2b, d-f, with a free b-, d-, e-, and f-propionic-acid function, respectively, were prepared by partial hydrolysis of heptamethyl Coα, Coβ -dicyanocobyrinate (cobester; 1) in aqueous sulfuric acid. The cobester monoacids 2b, d-f were obtained as a ca. 1:1:1:1 mixture which was separated. The monoacids were purified by chromatography and isolated in crystalline form. The position of the free propionic-acid function was determined by an extensive analysis of 2b, d-f using 2D-NMR techniques; an analysis of the C,H-coupling network topology resulted in an alternative assignment strategy for cobyrinic-acid derivatives, based on pattern recognition. Additional information on the structure of the most polar of the four hexamethyl cobyrinates, of the b-isomer 2b, was also obtained in the solid state from a single-crystal X-ray analysis. Earlier structural assignments based on 1D-NMR spectra of the corresponding regioisomeric monoamides 3b, d-f (obtained from crystalline samples of the monoacids 2b, d-f) were confirmed by the present investigations.

http://dx.doi.org/10.1002/hlca.19950780306