Ribitol, 2,4-dimethyl

CN 1 -deoxy-1 -[3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(27/)-yl]-D-ribitol... 

Pentadienone (divinyl ketone) was epoxidized55 by means of hydrogen peroxide in alkaline solution, to give a mixture of DL- and me.so-l,2 4,5-dianhydro-3-pentanones in the ratio of 13 7. Reduction of the ketone group in the DL-diepoxide with sodium horohvdride, followed by alkaline hydrolysis in dimethyl sulfoxide, was fully stereo-specific, and afforded DL-arabinitol. The same reaction-sequence performed on the meso-diepoxide led to a mixture of ribitol and xylitol. 

As shown in Figure 7.1, riboflavin consists of a tricyclic dimethyl-isoalloxazine ring conjugated to the sugar alcohol ribitol. The metabolically active coenzymes are riboflavin 5 -phosphate and flavin adenine dinucleotide (FAD). In some enzymes the prosthetic group is riboflavin, bound covalently at the catalytic site. 

The preparation of A -(4,5-dimethyl-2-nitrophenyl)-D-ribosylamine followed by hydrogenation to yield l-(2-amino-4,5-dimethylanilino)-l-deoxy-D-ribitol was also achieved. This compound is condensed with alloxan to form vitamin B2 (lactoflavin) [45] (Fig. 1). 

Riboflavin, also known as vitaniin B2, gets its name from its sugar alcohol (ribitol), and from its yellow color and its fluorescence under UV light (flavin comes from the Latin word for yellow). Its systematic names are 7,8-dimethyl-... 

In riboflavin (7,8-dimethyl-10-(/ )-ribityl isoalloxazine), the polyol ribitol is connected via an amino bond to the chromophore. Riboflavin is not an iV-gly-coside. Accordingly, flavin mononucleotide (FMN, riboflavin S -phosphate) and flavin adenine dinucleotide (FAD riboflavin 5 -adenosine diphosphate) are hydrolyzable only in the nucleotide part (Scheme 7.2.22). 

Riboflavin (vitamin B2) consists of a dimethyl-isoalloxazine nucleus combined with ribitol. Its structure is shown here ... 

Chemically, riboflavin may be described as a tricyclic, nitrogen-containing isoalloxazine ring-system with a ribitol side chain. Its systematic name is 7,8-dimethyl-10-(l-D-ribityl)-benzo[g]pteridin-2,4-dion, with an empirical formula of C17H20N4O6 and molecular weight of 376.36 g/mol. 

Condensation of dehydro-D-isoascorbic acid (dehydro-D-erythorbic acid) with one or two equivalents of l,2-diamino-4,5-dimethyl-benzene afforded a quinoxalinone, e.g. 81 or a quinoxaline, e.g, 82, respectively. An isomer of flavin adenine dinucleotide containing a D-arabinitol-l-yl rather than a D-ribitol-l-yl moiety, has been identified as a naturally occurring co-factor of the alcohol oxidase of methanol utilizing yeasts. ... 

Yellow (hence the name) prosthetic groups,//av/w adenine dinucleotide (FAD) and the somewhat less common flavin mononucleotide (FMN) are linked to protein in flavoproteins (Fig. 29), The nomenclature is not quite accurate since 6,7-dimethyl-isoalloxazine, which is responsible for the color, is not linked to ribose, as in the nucleotides, but to the corresponding sugar alcohol ribitol. In both FAD and FMN the 6,7-dimethyl-... 

Riboflavin is an isoalloxazine derivative, i.e. a pteridine ring with a benzene ring fused on to it. The side chain is a Cs-polyhydroxy group. Note that this is not an N-glycoside of ribose, but rather a derivative of ribitol, a pentahydroxy compound. The systematic name is 6,7-dimethyl-9-ribityl-isoalloxazine ... 

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