Vitamin B(12) and alpha-Ribonucleosides

Improved propionic acid and 5,6-dimethylbenzimidazole control strategy for vitamin B12 fermentation by Propionibacterium freudenreichii

An efficient fermentation-strengthening approach was developed to improve the anaerobic production of vitamin B12 by cultivation process optimization with Propionibacterium freudenreichii. The effects of the byproduct propionic acid and the precursor 5,6-dimethylbenzimidazole (DMB) on vitamin B12 biosynthesis were investigated. Byproduct inhibition experiments showed that maintaining propionic acid concentration in broth below 10-20 g/L in the early stage and 20-30 g/L in the late stage can efficiently improve vitamin B12 biosynthesis. Batch fermentation indicated the occurrence of feed-back inhibition in intracellular intermediate biosynthesis. In addition, the incorporation of the precursor DMB depended on the fermentation level of the vitamin B12 intermediate. High vitamin B12 concentration (58.8 mg/L) and production (0.37 mg/g) were obtained with an expanded bed adsorption bioreactor by using the propionic acid and DMB control method. The optimum concentration and production of 59.5 and 0.59 mg/L h for vitamin B12 production were respectively achieved after five continuous batches.

Peptide B12: emerging trends at the interface of inorganic chemistry, chemical biology and medicine

The sophisticated and efficient delivery of vitamin B(12) ("B(12)") into cells offers promise for B(12)-bioconjugates in medicinal diagnosis and therapy. It is therefore surprising that rather little attention is presently paid to an alternative strategy in drug design: the development of structurally perfect, but catalytically inactive semi-artificial B(12) surrogates. Vitamin B(12) cofactors catalyse important biological transformations and are indispensible for humans and most other forms of life. This strong metabolic dependency exhibits enormous medicinal opportunities. Inhibitors of B(12) dependent enzymes are potential suppressors of fast proliferating cancer cells. This perspective article focuses on the design and study of backbone modified B(12) derivatives, particularly on peptide B(12) derivatives. Peptide B(12) is a recently introduced class of biomimetic cobalamins bearing an artificial peptide backbone with adjustable coordination and redox-properties. Pioneering biological studies demonstrated reduced catalytic activity, combined with inhibitory potential that is encouraging for future efforts in turning natural cofactors into new anti-proliferative agents.

Guided cobalamin biosynthesis supports Dehalococcoides mccartyi reductive dechlorination activity

Dehalococcoides mccartyi strains are corrinoid-auxotrophic Bacteria and axenic cultures that require vitamin B12 (CN-Cbl) to conserve energy via organohalide respiration. Cultures of D. mccartyi strains BAV1, GT and FL2 grown with limiting amounts of 1 µg l(-1) CN-Cbl quickly depleted CN-Cbl, and reductive dechlorination of polychlorinated ethenes was incomplete leading to vinyl chloride (VC) accumulation. In contrast, the same cultures amended with 25 µg l(-1) CN-Cbl exhibited up to 2.3-fold higher dechlorination rates, 2.8-9.1-fold increased growth yields, and completely consumed growth-supporting chlorinated ethenes. To explore whether known cobamide-producing microbes supply Dehalococcoides with the required corrinoid cofactor, co-culture experiments were performed with the methanogen Methanosarcina barkeri strain Fusaro and two acetogens, Sporomusa ovata and Sporomusa sp. strain KB-1, as Dehalococcoides partner populations. During growth with H2/CO2, M. barkeri axenic cultures produced 4.2 ± 0.1 µg l(-1) extracellular cobamide (factor III), whereas the Sporomusa cultures produced phenolyl- and p-cresolyl-cobamides. Neither factor III nor the phenolic cobamides supported Dehalococcoides reductive dechlorination activity suggesting that M. barkeri and the Sporomusa sp. cannot fulfil Dehalococcoides' nutritional requirements. Dehalococcoides dechlorination activity and growth occurred in M. barkeri and Sporomusa sp. co-cultures amended with 10 µM 5',6'-dimethylbenzimidazole (DMB), indicating that a cobalamin is a preferred corrinoid cofactor of strains BAV1, GT and FL2 when grown with chlorinated ethenes as electron acceptors. Even though the methanogen and acetogen populations tested did not produce cobalamin, the addition of DMB enabled guided biosynthesis and generated a cobalamin that supported Dehalococcoides' activity and growth. Guided cobalamin biosynthesis may offer opportunities to sustain and enhance Dehalococcoides activity in contaminated subsurface environments.

Improvement of adenosylcobalamin production by metabolic control strategy in Propionibacterium freudenreichii

An efficient metabolic control approach was developed to improve the industrial anaerobic fermentation of adenosylcobalamin (ado-cbl) by Propionibacterium freudenreichii. The effects of 5,6-dimethylbenzimidazole (DMB) on cell growth and ado-cbl biosynthesis were investigated. Subsequently, the results obtained from the batch culture showed that an important intermediate of ado-cbl separated from the cell extract was identified as adenosylcobinamide (ado-cbi) by high-performance liquid chromatography coupled to an ultraviolet diode array detector and ESI mass spectrometry analysis. Ado-cbi can be converted to ado-cbl when linked to DMB, which is an essential compound for ado-cbi bioconversion. This key ado-cbi is useful not only in determining ado-cbl concentration in the fermentation process but also in serving as an effective compound to guide DMB incorporation for the harvest of the maximum ado-cbl concentration. Accordingly, with scaling up to 100 L fermentation, the experimental results showed that the discrepancy was less than 1 % using the developed prediction technique. Overall, the findings show that the method is efficient in evaluating the fermentation of ado-cbl by propionibacteria.

Chemoselective deprotection of triethylsilyl ethers

An efficient and selective method was developed for the deprotection of triethylsilyl (TES) ethers using formic acid in methanol (5-10%) or in methylene chloride 2-5%) with excellent yields. TES ethers are selectively deprotected to the corresponding alcohols in high yields using formic acid in methanol under mild reaction conditions. Other hydroxyl protecting groups like t-butyldimethylsilyl (TBDMS) remain unaffected.