✍ Scribed by Prof. Dr. Shahzad Murtaza; Markus Ruetz; Prof. Dr. Karl Gruber; Prof. Dr. Bernhard Kräutler
No coin nor oath required. For personal study only.
Vitamin B 12 (cyanocobalamin, 1) features a cobalt corrin and a nucleotide functionality in the stable, "base-on" form, [1][2][3] a hallmark of Natures "most beautiful" cofactors. [4] The intramolecular coordination of the nucleotide appendage to the corrin-bound cobalt center gives a unique threedimensional structure [1] and modulates the reactivity of the cobalt center. [5] The complexity of 1 has been considered an impressive challenge for the (current understanding on the) evolution of the catalytic moieties of essential cofactors. According to Eschenmoser, the natural corrinoids may represent a further evolved form of the hypothetical B 12 progenitor "protocobyrinic acid" and the seemingly specific nucleotide loop of 1 may have arisen from adaptation and (non-enzymatic) self-constitution. [6] This loop is a specific structural selection element for recognition by proteins involved in controlled B 12 uptake [7] or by the protein parts of some B 12dependent enzymes. [8] We report on isovitamin B 12 (2, Co b -cyano-5'',6''-dimethylbenzimidazolyl-176-isocobamide, see Figure 1), [9] an isomer of vitamin B 12 , in which n-propanolamine constitutes the linker, rather than (R)-isopropanolamine. Our studies were induced by the discovery of nor-pseudovitamin B 12 , the natural "complete" B 12 cofactor (with an ethanolamine linker) of perchloroethylene reductase from Sulfurospirillum multivorans. [10] The corresponding cobalamin analogue, norvitamin B 12 (3, see Scheme 1), was synthesized in more recent studies in this area, [11] and turned out to be a natural corrinoid also, which was detected in Salmonella sp. [12] Isovitamin B 12 (2) was prepared by the method [9,13] outlined for the partial synthesis of norvitamin B 12 (3). [11] It was obtained in 65 % yield by condensation of cobyric acid (4) [9,14] and (3-aminopropyl)-3'-a-ribazolyl-diphosphate (5) (see Scheme 1, Experimental Section and Supporting Information) and recrystallization from aqueous acetone. The chromatographic behavior of 2 was similar to that of vitamin B 12 (1), and the UV/Vis spectra of 1 and of its isomer 2 were practically indistinguishable. [15] FAB-mass spectra exhibited a pseudo-molecular ion at m/z 1355, that is, at the same value as that of 1. UV/Vis and 1 H NMR spectra, as [a] Prof.
📜 SIMILAR VOLUMES
## Abstract Incorporation of the lipophilic Co(III)‐cobyrinate octadecyl‐cobester **1** and of its ionic aqua‐cyano perchlorate derivative **2** into poly(vinyl chloride)/bis(1‐butylpentyl) adipate liquid membranes induces a selectivity, measured potentiometrically, of about 10^3^ for SCN^−^ an NO