Keith ó Proinsias

New hydrophobic vitamin B12 derivatives via ring-opening reactions of c-lactone.

A selective synthesis of new hydrophobic cobalamin derivatives bearing two different spacers has been accomplished via ring-opening reaction of c-lactone. The reaction of c-lactone with various amines afforded three types of amides (a, b, and c) depending on the reaction conditions. The structure of lactone b was determined by the X-ray analysis confirming the position of ring closure. It also reveals the presence of a hydrogen bond between the terminal hydroxy group and one of the axial cyanide ligands.

Synthesis of New Hydrophilic and Hydrophobic Cobinamides as NO- Independent sGC Activators

Herein, the synthesis of novel hydrophobic and hydrophilic cobinamides via aminolysis of vitamin B12 derivatives that activate soluble guanyl cyclase (sGC) is presented. Unlike other sGC regulators, they target the catalytic domain of sGC and show higher activity than (CN)2Cbi.

Cobryketone Derived from Vitamin B12via Palladium-Catalyzed Cleavage of the sp3–sp3 Carbon–Carbon Bond

Heptamethyl cobyrinate was transformed into hexamethyl 8-nor-cobyrinate. The crucial step involved the synthesis of new, vitamin B12 derived cobryketone via palladium-catalyzed cleavage of the sp(3)-sp(3) carbon-carbon bond with the liberation of the ketone. The replacement of sp(3) carbon atom with sp(2) (C═O) at the 8-position produces a bathochromic shift of all absorption bands and makes α and β bands equal as a consequence of the expansion of the existing conjugated system of double bonds.

Microwave-Assisted Cobinamide Synthesis

We present a new method for the preparation of cobinamide (CN)2Cbi, a vitamin B12 precursor, that should allow its broader utility. Treatment of vitamin B12 with only NaCN and heating in a microwave reactor affords (CN)2Cbi as the sole product. The purification procedure was greatly simplified, allowing for easy isolation of the product in 94% yield. The use of microwave heating proved beneficial also for (CN)2Cbi(c-lactone) synthesis. Treatment of (CN)2Cbi with triethanolamine led to (CN)2Cbi(c-lactam).

Synthesis and Evaluation of Bifunctional sGC Regulators: Optimization of a Connecting Linker

Hybrid molecules composed of PpIX and cobyrinic acid derivatives conjugated through linkers of varying length and composition were prepared via 1,3-dipolar cycloaddition (CuAAC) or amidation/esteryfication reactions. They were tested for activation of soluble guanylyl cyclase (sGC), a key enzyme in the NO/cGMP signaling pathway, by an in vitro GTP→cGMP conversion assay. Using purified heme-deficient sGC and truncated sGC variants lacking a heme-binding domain, we demonstrated that such hybrid molecules may activate sGC by targeting heme-binding and/or catalytic domain. While all conjugates activated sGC, only selected compounds served as bifunctional regulators and were capable of simultaneous targeting both heme and catalytic domains of sGC. The length and type of a linker connecting both components had a profound effect on the extent of sGC activation, indicating that the linkers type is crucial for their binding affinities with regulatory and catalytic domains. Only hybrids with the conjugated linker of 13-16 atom length synergistically target both domains and displayed the lowest EC50 and highest activating potency. Compounds with shorter connecting linkers were much less potent and were no more active than the cobyrinic acid component alone. The most active conjugate, which showed a 60-fold activation of sGC, was compound 11, in which PpIX and cobyrinic acid components are separated by 11 atoms chain with the triazole moiety in between.

Vitamin B12 Derivatives as Activators of Soluble Guanylyl Cyclase

Various newly prepared and previously known vitamin B₁₂ derivatives have been studied as potential soluble guanylyl cyclase (sGC) activators. All compounds tested were found to activate the sGC enzyme, although to differing extents. The best results were obtained with the derivatives synthesized from c-lactone and possessing aliphatic amides in the c- and d-positions.

Selective modifications of hydrophobic vitamin B12 derivatives at c-and d-positions.

The acid-sensitivity of vitamin B(12) derived mono- and diamides was studied. It was found that the use of reductive ring-opening of the lactone moiety deactivated undesired decomposition of c-mono- and c,d-diamides under acidic conditions. As a result, reactions gave respectively c- or d-acids which were further functionalized via coupling with amino acids. Though mono- and diamides exhibited acid sensitivity, they were used for the preparation of several highly functionalized molecules showing their stability under various reaction conditions.

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.

Vitamin B12 Catalysis: Probing the Structure/Efficacy Relationship

Vitamin B12 is a cofactor for many enzymes, but it also functions as a catalyst in C-C bond-forming reactions. Herein, the impact of corrin structural modifications on their catalytic efficacy was examined. Derivatives with various substituents at c-, d-, and meso-positions were synthesised by using traditional and new microwave methodologies, and then tested in the model reaction of 1,1-diphenylethylene with ethyl diazoacetate. To complement the experimental data, cyclic voltammetry and DFT calculations were performed. Mainly alterations at the c- or d-positions influence both the reaction yield and selectivity.

Vitamin B12 Phosphate Conjugation and Its Effect on Binding to the Human B12 -Binding Proteins Intrinsic Factor and Haptocorrin.

The binding of vitamin B12 derivatives to human B12 transporter proteins is strongly influenced by the type and site of modification of the cobalamin original structure. We have prepared the first cobalamin derivative modified at the phosphate moiety. The reaction conditions were fully optimized and its limitations examined. The resulting derivatives, particularly those bearing terminal alkyne and azide groups, were isolated and used in copper-catalyzed alkyne-azide cycloaddition reactions (CuAAC). Their sensitivity towards light revealed their potential as photocleavable molecules. The binding abilities of selected derivatives were examined and compared with cyanocobalamin. The interaction of the alkylated derivatives with haptocorrin was less affected than the interaction with intrinsic factor. Furthermore, the configuration of the phosphate moiety was irrelevant to the binding process.