Reaction of Dicyanocobyrinic Heptamethyl Ester with Ascorbic Acid

Abstract

Most reactions of cyanocobalamin (vitamin Biz) which proceed with alteration of the oxidation state of the complexbonded cobalt ion are accompanied by the formation of by-products which are called stable yellow corrinoids['! Despite numerous attempts, it has not previously proved possible to elucidate the structure of these compounds. Owing to the biological (metabolism of the vitamin B1 2-coenzyme in the living cell) and pharmacological interest (incompatibility of cyanocobalamin and vitamin C in mixtures of vitamins), we have investigated the formation of such pigments by treating dicyanocobyrinic heptamethyl ester ( I )[' I with ascorbic acid. As the former is readily soluble in aprotic solvents, its use as substrate is more advantageous from the preparative and analytical point of view.Thus, reaction of a solution of ( 1 ) in methanol-water with ascorbic acid in the presence of oxygen yields a yellow cor-

A Nickel(II)‐Containing Vitamin B12 Derivative with a Cofactor‐F430‐type π‐System

“…Carbon atoms associated with the "northern" part of the corrin macrocycle were detected at 201.4 (C4), 33.9 (C51), and 176.5 ppm (C6), respectively.T he remarkable downfield shifts (Dd = 9.7-17 ppm) compared to 1-OH 2 + agree with the expected deshielding effects of the two adjacent hydroxy groups at C5 and C6. [32,33] Based on this comparison, we tentatively assigned the OH group at C6 to be directed towards the a side (S configuration), that is,intrans position to the adjacent OH group located at C5 (Figures 5a nd S4 [24] ). [31] Thes tereochemistry at positions C5 and C6 of the reconstituted macrocycle was addressed with 1 H-1 HROESY spectroscopy ( Figure 5).…”

“…Evidence for the absolute configuration at C6 was then obtained by circular dichroism (CD) spectroscopy.The CD spectrum of metal-free 3 between 250 and 430 nm ( Figure S3 [24] )is(almost) identical to that of ayellow 5R,6S-dihydroxycorrinoid, but fundamentally different to that of ar elated 5R,6R isomer (Figure S4 [24] ). [32,33] Based on this comparison, we tentatively assigned the OH group at C6 to be directed towards the a side (S configuration), that is,intrans position to the adjacent OH group located at C5 (Figures 5a nd S4 [24] ). In our studies,r emarkable similarities in the UV/Vis and 13 CNMR spectra of 4 and F430 were observed despite major structural differences in terms of the size and constitutional details of the two tetradentate macrocycles.T he spectral resemblances are explained by some common structural features of the compounds (Figure 1).…”

Pulse Radiolysis and Ultra‐High‐Performance Liquid Chromatography/High‐Resolution Mass Spectrometry Studies on the Reactions of the Carbonate Radical with Vitamin B12 Derivatives

“…At ypical mass spectrum for one of the peaks of the UV/Vis chromatogram and the corresponding mass spectrum simulationi ss hown in Figure S11, Supporting Information. The c-lactone derivativeo fB 12 is well-known, Figure 12, [26] with aU V/Vis spectrum that is similar to the parentB 12 complex. [27] Note that our experimental data does not tell us at which ring positions lactone formation occurs nor the position at which two or four hydrogen atoms are abstracted.…”

Ein NiII‐haltiges Vitamin‐B12‐Derivat mit einem Kofaktor‐F430‐artigen π‐System

“…Das CD-Spektrum des metallfreien 3 ist zwischen 250 und 430 nm weitestgehend identisch mit dem Spektrum eines bereits bekannten gelben 5R,6S-Dihydroxycorrinoids (Abbildung S3 [24] ), unterscheidet sich jedoch fundamental vom Spektrum eines verwandten 5R,6R-Isomers (Abbildung S4 [24] ). [32,33] Aufd er Grundlage des Vergleichs der CD-Spektren folgerten wir, dass die OH-Gruppe an Position C6 in Richtung der a-Seite ausgerichtet ist (S-Konfiguration), d. h. in trans-Anordnung zur benachbarten OH-Gruppe an Position C5 steht (Abbildungen 5und S4 [24] ). Unsere Untersuchungen legen bemerkenswerte Gemeinsamkeiten in den UV/Vis-und 13 C-NMR-Daten von 4 und F430 offen, obwohl sich die beiden vierzähnigen Makrozyklen in ihrer Grçße und einigen Details ihrer Konstitution maßgeblich unterscheiden.…”