Synthesis of a B Ring Opened 7,8-seco-Vitamin B12 Derivative with Grob Fragmentation

The inorganic chemistry of the cobalt corrinoids - an update

The inorganic chemistry of the cobalt corrinoids, derivatives of vitamin B₁₂, is reviewed, with particular emphasis on equilibrium constants for, and kinetics of, their axial ligand substitution reactions. The role the corrin ligand plays in controlling and modifying the properties of the metal ion is emphasised. Other aspects of the chemistry of these compounds, including their structure, corrinoid complexes with metals other than cobalt, the redox chemistry of the cobalt corrinoids and their chemical redox reactions, and their photochemistry are discussed. Their role as catalysts in non-biological reactions and aspects of their organometallic chemistry are briefly mentioned. Particular mention is made of the role that computational methods - and especially DFT calculations - have played in developing our understanding of the inorganic chemistry of these compounds. A brief overview of the biological chemistry of the B₁₂-dependent enzymes is also given for the reader's convenience.

Functionalisation of vitamin B12 derivatives with a cobalt β-phenyl ligand boosters antimetabolite activity in bacteria

This study describes the syntheses of four singly- and two doubly-modified vitamin B₁₂ derivatives for generating antimetabolites of Lactobacillus delbrueckii (L. delbrueckii). The two most potent antagonists, a Co_β-phenyl-cobalamin-c,8-lactam and a 10-bromo-Co_β-phenylcobalamin combine a c-lactam or 10-bromo modification at the “eastern” site of the corrin ring with an artificial organometallic phenyl group instead of a cyano ligand at the β-site of the cobalt center. These two doubly-modified B₁₂ antagonists (10 nM) inhibit fully B₁₂-dependent (0.1 nM) growth of L. delbrueckii. In contrast to potent 10-bromo-Co_β-phenylcobalamin, single modified 10-bromo-Co_β-cyanocobalamin lacking the artificial organometallic phenyl ligand does not show any inhibitory effect. These results suggest, that the organometallic β-phenyl ligand at the Co center ultimately steers the metabolic effect of the 10-bromo-analogue.

This study describes the syntheses of four singly- and two doubly-modified vitamin B₁₂ derivatives for generating antimetabolites of Lactobacillus delbrueckii (L. delbrueckii).

Synthesis of (2-(Quinolin-2-yl)phenyl)carbamates by a One-Pot Friedel-Crafts Reaction/Oxidative Umpolung Aza-Grob Fragmentation Sequence

Utilizing the easily available isatin-based propargyl amines prepared from isatins, terminal alkynes, and anilines, (2-(quinolin-2-yl)phenyl)carbamates were prepared by a one-pot reaction in sequence, combining the gold-catalyzed Friedel-Crafts cyclization, oxidative umpolung aza-Grob fragmentation, and nucleophilic addition. In this process, gold-catalyzed cyclization of isatin-based propargyl amines gave 1'H-spiro[indoline-3,2'-quinolin]-2-ones, which were oxidized in situ by hypervalent iodine via the aza-Grob fragmentation to afford isocyano intermediates 2-(2-isocyanatophenyl)quinolines. Followed by the nucleophilic addition with alcohol solvents, (2-(quinolin-2-yl)phenyl)carbamates were synthesized. This procedure features easy operation, a wide substrate scope, and mild conditions.

Modified biovectors for the tuneable activation of anti-platelet carbon monoxide release

This communication describes the anti-platelet effects of a new class of cis-rhenium(ii)-dicarbonyl-vitamin B₁₂ complexes (B₁₂-ReCORMs) with tuneable CO releasing properties.

Effect of bridgehead substitution in the Grob fragmentation of norbornyl ketones: a new route to substituted halophenols

Grob fragmentation of suitably designed bicyclic species often generates novel organic skeletons in a facile manner. Herein, we report a comprehensive account of an effective acid-catalyzed Grob fragmentation of trihalonorbornyl ketones to dihalophenol derivatives in good yields. The transformation entails tri-n-butyltin hydride (TBTH) mediated regioselective reduction of one of the two bridgehead halogens of readily available Diels-Alder adducts resulting from 1,2,3,4-tetrahalo-5,5-dimethoxycyclopentadiene and vinyl acetate derivatives, followed by its conversion to substituted halophenol species via a three-step hydrolysis-oxidation-rearrangement/aromatization strategy. Both alkyl and aryl substituted norbornyl ketones were studied. A detailed mechanistic analysis employing an isotope labeling experiment revealed plausible mechanistic pathways. Among the two bridgehead substituents, when halogen (X = Cl, Br) stays at C-1 and hydrogen (H, or deuterium, D) at C-4, then product formation takes place via exclusive protonation (supplied by an external acid) at β carbon (i.e. C-1) of a dienol moiety formed in situ during the Grob-fragmentation, followed by the removal of acidic 4-H (or 4-D) and halide ion (X(-)) from the resulting cyclohexenone intermediate prior to nucleophilic attack on the oxocarbenium ion by X(-) and final enolisation of cyclohexadienone species. A sharp deviation was observed with the regioisomeric bicyclic ketone, wherein the 4-X triggers a facile removal of X(-) and forms the end products without necessitating the involvement of the C-1 substituent (i.e. 1-H/D), thereby retaining it in the final halophenols. It clearly demonstrates how the bridgehead substituents in the two regioisomeric trihalo-norbornyl ketones steer the bicyclic systems to follow entirely different reaction pathways thus suggesting their crucial yet distinct roles in the overall reaction. The present transformation thus manifests the relevance of bridgehead substituents in the Grob fragmentation of such norbornyl systems. Our current strategy also allows one to access ortho-deuterated halophenol compounds.

Antivitamins for Medicinal Applications

Antivitamins represent a broad class of compounds that counteract the essential effects of vitamins. The symptoms triggered by such antinutritional factors resemble those of vitamin deficiencies, but can be successfully reversed by treating patients with the intact vitamin. Despite being undesirable for healthy organisms, the toxicities of these compounds present considerable interest for biological and medicinal purposes. Indeed, antivitamins played fundamental roles in the development of pioneering antibiotic and antiproliferative drugs, such as prontosil and aminopterin. Their development and optimisation were made possible by the study, throughout the 20th century, of the vitamins' and antivitamins' functions in metabolic processes. However, even with this thorough knowledge, commercialised antivitamin-based drugs are still nowadays limited to antagonists of vitamins B9 and K. The antivitamin field thus still needs to be explored more intensely, in view of the outstanding therapeutic success exhibited by several antivitamin-based medicines. Here we summarise historical achievements and discuss critically recent developments, opportunities and potential limitations of the antivitamin approach, with a special focus on antivitamins K, B9 and B12 .

Functionalized α,α-dibromo esters through Claisen rearrangements of dibromoketene acetals

Allylic alcohols can be transformed into γ,δ-unsaturated α,α-dibromo esters through a two-step process: formation of a bromal-derived mixed acetal, followed by tandem dehydrobromination/Claisen rearrangement. The scope and selectivity of both steps have been investigated. The product α,α-dibromo esters were subjected to various carbon-carbon bond-forming reactions, oxidations, and lactonizations.

Small alterations in cobinamide structure considerably influence sGC activation

Specially designed B-ring-modified cobalamin derivatives were synthesized and tested as potential activators of soluble guanylyl cyclase (sGC). Herein, we disclose the influence of substituents at the c- and d-positions in hydrophilic and hydrophobic cobyrinic acid derivatives on their capacities to activate sGC. The presence of the amide group at c-/d-position in cobyrinic acid derivatives strongly influence the level of sGC activation. Removal of the d-position altogether has a profound effect for hydrophobic compounds. In contrast, little differences were observed in hydrophilic ones.