“Clickable” Vitamin B12 Derivative

A “clickable” vitamin B₁₂ derivative possessing the azide functionality at the 5′‐position was synthesized by means of a two‐step procedure on the gram scale. The reaction of cobalamin with mesyl chloride (MsCl) afforded the 5′‐OMs derivative, which was subsequently transformed to the desired 5′‐azide, the structure of which was confirmed using X‐ray analysis. It proved to be reactive in the azide–alkyne 1,3‐dipolar cycloaddition reaction to give substituted triazoles in high yields. A study of the reaction conditions and the scope of the process are reported.     

Organometallic B12–DNA Conjugate: Synthesis,Structure Analysis,and Studies of Binding to Human B12‐Transporter Proteins

Design, synthesis, and structural characterization of a B₁₂‐octadecanucleotide are presented herein, a new organometallic B₁₂–DNA conjugate. In such covalent conjugates, the natural B₁₂ moiety may be a versatile vector for controlled in vivo delivery of oligonucleotides to cellular targets in humans and animals, through the endogenous B₁₂ transport systems. Binding of the organometallic B₁₂ octadecanucleotide to the three important human proteins of B₁₂ transport was studied, to examine its structural suitability for the task of eventual in vivo oligonucleotide delivery. Binding was efficient with transcobalamin (TC), but not so efficient with the homologous glycoproteins intrinsic factor and haptocorrin. Binding of the B₁₂ octadecanucleotide to TC suggests the capacity of the B₁₂ moiety to serve as a natural vector for specific transport of single stranded, organometallic oligonucleotide loads from the blood stream into cells.     

7‐Decarboxymethyl‐cobyrinates: Vitamin B12‐Derivatives that Lack the c‐Side Chain

The synthesis of cobyrinic acid derivatives by reduction of dehydrocobyrinates is largely unexplored. It is, however, a rational path to B₁₂ analogues that lack specific substituents of the corrin moiety of natural B₁₂ derivatives. The partial syntheses of four epimeric 7‐decarboxymethyl‐cobyrinates is described, which is achieved by reduction of Δ7‐dehydro‐7‐de[carboxymethyl]‐cobyrinate with zinc or with the ‘prebiotic’ reducing agent formic acid. A direct and remarkably efficient route was found to 7‐decarboxymethyl‐cobyrinates, which are cobyrinic acid derivatives in which the c‐side chain at ring B of vitamin B₁₂ is missing. The structures of the hexamethyl‐7‐decarboxymethyl‐cobyrinates were characterized and the stereochemical and conformational properties at their newly saturated ring B were analyzed. The stereochemical outcome of the reduction was found to depend strongly on the reaction conditions. In 7‐decarboxymethyl‐cobyrinates, both peripheral carbon centres of ring B carry a hydrogen atom, and the characteristic quaternary carbon centre at C7 of the cobyrinic acid moiety of vitamin B₁₂ is lacking. The still highly substituted 7‐decarboxymethyl‐cobyrinates are readily dehydrogenated in the presence of dioxygen, furnishing 7‐de[carboxymethyl]‐Δ⁷‐dehydro‐cobyrinate as the common, unsaturated oxidation product. The noted stability of vitamin B₁₂ and of other Co^III‐cobyrinates in the presence of air is a consequence of their highly substituted corrin macrocycle, a finding of interest in the context of chemical rationalizations of the B₁₂ structure.     

Antivitamin B12 Inhibition of the Human B12-Processing Enzyme CblC: Crystal Structure of an Inactive Ternary Complex with Glutathione as the Cosubstrate

B₁₂ antivitamins are important and robust tools for investigating the biological roles of vitamin B₁₂. Here, the potential antivitamin B₁₂ 2,4-difluorophenylethynylcobalamin (F2PhEtyCbl) was prepared, and its 3D structure was studied in solution and in the crystal. Chemically inert F2PhEtyCbl resisted thermolysis of its Co−C bond at 100 °C, was stable in bright daylight, and also remained intact upon prolonged storage in aqueous solution at room temperature. It binds to the human B₁₂-processing enzyme CblC with high affinity (K_D=130 nm ) in the presence of the cosubstrate glutathione (GSH). F2PhEtyCbl withstood tailoring by CblC, and it also stabilized the ternary complex with GSH. The crystal structure of this inactivated assembly provides first insight into the binding interactions between an antivitamin B₁₂ and CblC, as well as into the organization of GSH and a base-off cobalamin in the active site of this enzyme.     

Homocoenzyme B12 and Bishomocoenzyme B12: Covalent Structural Mimics for Homolyzed,Enzyme‐Bound Coenzyme B12

Efficient electrochemical syntheses of “homocoenzyme B₁₂” ( 2 , Co_β‐(5′‐deoxy‐5′‐adenosyl‐methyl)‐cob(III )alamin) and “bishomocoenzyme B₁₂” ( 3 , Co_β‐[2‐(5′‐deoxy‐5′‐adenosyl)‐ethyl]‐cob(III )alamin) are reported here. These syntheses have provided crystalline samples of 2 and 3 in 94 and 77 % yield, respectively. In addition, in‐depth investigations of the structures of 2 and 3 in solution were carried out and a high‐resolution crystal structure of 2 was obtained. The two homologues of coenzyme B₁₂ ( 2 and 3 ) are suggested to function as covalent structural mimics of the hypothetical enzyme‐bound “activated” (that is, “stretched” or even homolytically cleaved) states of the B₁₂ cofactor. From crude molecular models, the crucial distances from the corrin‐bound cobalt center to the C5′ atom of the (homo)adenosine moieties in 2 and 3 were estimated to be about 3.0 and 4.4 Å, respectively. These values are roughly the same as those found in the two “activated” forms of coenzyme B₁₂ in the crystal structure of glutamate mutase. Indeed, in the crystal structure of 2 , the cobalt center was observed to be at a distance of 2.99 Å from the C5′ atom of the homoadenosine moiety and the latter was found to be present in the unusual syn conformation. In solution, the organometallic moieties of 2 and 3 were shown to be rather flexible and to be considerably more dynamic than the equivalent group in coenzyme B₁₂. The homoadenosine moiety of 2 was indicated to occur in both the syn and the anti conformations.     

Li2B12 and Li3B12: Prediction of the Smallest Tubular and Cage‐like Boron Structures

An intriguing structural transition from the quasi‐planar form of B₁₂ cluster upon the interaction with lithium atoms is reported. High‐level computations show that the lowest energy structures of LiB₁₂, Li₂B₁₂, and Li₃B₁₂ have quasi‐planar (C_s), tubular (D_6d), and cage‐like (C_s) geometries, respectively. The energetic cost of distorting the B₁₂ quasi‐planar fragment is overcompensated by an enhanced electrostatic interaction between the Li cations and the tubular or cage‐like B₁₂ fragments, which is the main reason of such drastic structural changes, resulting in the smallest tubular (Li₂B₁₂) and cage‐like (Li₃B₁₂) boron structures reported to date.     

Oxygen‐Controlled Catalysis by Vitamin B12‐TiO2: Formation of Esters and Amides from Trichlorinated Organic Compounds by Photoirradiation

An oxygen switch in catalysis of the cobalamin derivative (B₁₂)‐TiO₂ hybrid catalyst for the dechlorination of trichlorinated organic compounds has been developed. The covalently bound B₁₂ on the TiO₂ surface transformed trichlorinated organic compounds into an ester and amide by UV light irradiation under mild conditions (in air at room temperature), while dichlorostilbenes (E and Z forms) were formed in nitrogen from benzotrichloride. A benzoyl chloride was formed as an intermediate of the ester and amide, which was detected by GC‐MS. The substrate scope of the synthetic strategy is demonstrated with a range of various trichlorinated organic compounds. A photo‐duet reaction utilizing the hole and conduction band electron of TiO₂ in B₁₂‐TiO₂ for the amide formation was also developed.     

Synthesis and Irradiation of Vitamin‐B12‐Derived Complexes Incorporating Peripheral G⋅C Base Pairs

The vitamin‐B₁₂ derivative 11 , incorporating a peripheral N⁴‐acetylcytosine moiety, was alkylated under reductive conditions with 2‐(iodomethyl)‐2‐methylmonothiomalonate 8 bearing the complementary guanine moiety. The reaction yielded a mixture of vitamin‐B₁₂‐derived complexes with variations in the cytosine moiety: products 16 – 18 with a cytosine, a N⁴‐acetylated cytosine, and a N⁴‐acetylated reduced cytosine moiety were formed (see Scheme 5). The complexes were photolyzed in CHCl₃/MeCN to yield the dimethylmalonate derivative 22 (Scheme 6) but not the rearranged succinate, in contrast to the results obtained earlier with complexes incorporating the A⋅T base pair (see Scheme 1).     

Penicillamine functionalized B12N12 and B12CaN12 nanocages act as potential inhibitors of proinflammatory cytokines: A combined DFT analysis,ADMET and molecular docking study

The adsorption of penicillamine (PCA) on pure B₁₂N₁₂ and B₁₂CaN₁₂ nanocages in aqueous and chloroform solvents has been evaluated using density functional theory (DFT) calculations. The interaction of PCA on B₁₂N₁₂ nanocages is chemisorption through its four nucleophilic sites: amine, carbonyl, hydroxyl and thiol. The most stable adsorption configuration was achieved when zwitterionic PCA adsorbs via its carbonyl group in water with value of ?1.723 eV, in contrast, when neutral PCA adsorbs via its amine group in chloroform with value of ?1.68 eV. Intercalated calcium ion within B₁₂N₁₂ nanocage (B₁₂CaN₁₂) was shown to attract PCA onto nanocage surface, resulting in higher solubility and adsorption energy after their complexation in water and chloroform. The adsorption of multiple PCA molecules from their amine and carbonyl groups on pure and B₁₂CaN₁₂ nanocages were also evaluated where two and three molecules can be chemisorbed on boron atoms of the nanocage surfaces with the adsorption energy per PCA reduces slightly with the increasing the amount of drugs due to the curvature effects. Molecular docking study indicates that PCA from its NH₂ group on B₁₂CaN₁₂ nanocage has the best binding affinity and inhibition potential of tumor necrosis factor-alpha (TNF-α) and Interleukin-1 (IL-1) receptors as compared with the other adsorption systems. Molecular docking and ADMET analysis displayed that the chosen compounds pass Lipinski Rule and have appropriate pharmacokinetic features suitable as models for developing anti-inflammatory agents.     

Determination of Cobalt in the Form of an Ion Associate in Vitamin B<Subscript>12</Subscript>

The possibility of application of the ion-associated complex formed between the anionic chelate cobalt(II)-4-(2-thiazolylazo) resorcinol (TAR) with the cation of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) for extraction-spectrophotometric determination of cobalt in the form of an ion associate in Vitamin B₁₂ was studied. The liquid–liquid extraction system Co(II)-TAR-MTT-H₂O-CHCl₃ was applied. This system was chosen by our previous research of the ion associates of the cobalt by spectrophotometric investigation of fourteen different liquid–liquid extraction systems, containing azo derivatives of resorcinol (TAR or 4-(2-pyridylazo) resorcinol (PAR)) and mono or ditetrazolium salts. Based on the obtained results, a sensitive, relatively simple, convenient and inexpensive method for determination of cobalt in the form of an ion associate in Vitamin B₁₂ was developed. The proposed method can be implemented for biological, medical and pharmaceutical samples containing cobalamin (Vitamin B₁₂).     

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12Cl11]−

It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B₁₂Cl₁₁]⁻ spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of “superelectrophilic” dications. [B₁₂Cl₁₁Ng]⁻ adducts, with Ng binding energies of 80 to 100 kJ mol⁻¹, contain B−Ng bonds with a substantial degree of covalent interaction. The electrophilic nature of the [B₁₂Cl₁₁]⁻ anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B₁₂Cl₁₁CO]⁻ and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B₁₂Cl₁₁]⁻ results in an energy barrier for the approach of polar molecules and facilitates the formation of Ng adducts that are not detected with reactive cations such as [C₆H₅]⁺. This introduces the new chemical concept of “dipole-discriminating electrophilic anions.”     

Synthesis and Structure of Vitamin B<Subscript>12</Subscript>-Derivatives with a Modified Ribose-Unit

Summary. The acylation at the 5′-OH group of the ribose-unit of vitamin B₁₂ (cyanocobalamin) or of aquocobalamin with two conventional reagents gave mono-acylated B₁₂-derivatives with good to very high selectivity. The site of the modification was deduced from spectral data of the products and was further supported by the crystal structure data of three such modified B₁₂-derivatives. These three B₁₂-derivatives were found to crystallize in the space group P2₁2₁2₁, irrespective of the nature of the appendage. Acylation at 5′-OH has been used to protect (or block) this group in the context of functionalization of 2′-OH or elsewhere in the B₁₂-molecule. Attachment of the bifunctional succinyl-unit has allowed the preparation of further modified derivatives of vitamin B₁₂ and binding of B₁₂-derivatives to biological carriers and other macromolecules. In aqueous solution, 5′-acylcobalamins turned out to be rather susceptible to hydrolytic loss of the acyl-functionality. Bernhard Kr?utler: In memoriam Prof. Karl Schl?gl     

Synthesis of Oligomeric Mannosides and Their Structure‐Binding Relationship with Concanavalin A

Small glycodendrimers with α‐mannosyl ligands were synthesized by using copper‐catalyzed azide–alkyne coupling chemistry and some of these molecules were used as multivalent ligands to study the induction of concanavalin A (Con A) precipitation. The results showed that the monovalent mannose ligand could induce the precipitation of Con A. This unexpected finding initiated a series of studies to characterize the molecular basis of the ligand–lectin interaction. The atypical precipitation is found to be specific to the mannose, fluorescein moiety (FITC), and Con A. Apparently the mannose ligand binds to Con A through hydrogen‐bonding interactions, whereas the binding of FITC is mediated by hydrophobic forces.     

The electronic structure ofα-B12, B12P2 and B12AS2

The electronic band structures of the rhombohedral-based boron compounds -B₁₂, B₁₂P₂ and B₁₂ As₂ have been investigated along all symmetry directions. The calculations show that the band gap, in all cases, is of the order of 2 eV, which correlates with the known color of -rhombohedral boron. The materials should be intrinsic semi-conductors, as has recently been shown experimentally. The states around the band gap in -B₁₂ are dominated by the boron 2p atomic states. The bonding in the icosahedra, as illuminated by cluster calculations, is shown to be rather similar to that in the isolated B₁₂ icosahedron. Of the intericosahedron interactions, those between B(2) and B(2) atoms are the strongest and have a bond index just above unity. In B₁₂P₂ the orbitals of the P₂ moiety make a significant contribution to the valence band edge states and the conduction band edge states also incorporate considerable (55%) phosphorus 3d orbital character. In B₁₂As₂ the arsenic 4d orbitals do not have as much effect in that crystal as do the 3d orbitals in B₁₂P₂.     

Calixarene‐centered amphiphilic A2B2 miktoarm star copolymers based on poly(ε‐caprolactone) and poly(ethylene glycol): Synthesis and self‐assembly behaviors in water

Novel calixarene‐centered amphiphilic A₂B₂ miktoarm star copolymers composed of two PCL arms and two PEG arms with calix[4]arene as core moiety were synthesized by the combination of CROP and “click” chemistry. First, a heterotetrafunctional calix[4]arene derivative with two hydroxyl groups and two alkyne groups was designed as a macroinitiator to prepare calixarene‐centered PCL homopolymers (C4‐PCL) by CROP in the presence of Sn(Oct)₂ as catalyst at 110 °C. Next, azide‐terminated PEG (A‐PEG) was synthesized by tandem treating methoxy poly(ethylene glycol)s (mPEG) with 4‐chlorobutyryl chloride and NaN₃. Finally, copper(I)‐catalyzed cycloaddition reaction between C4‐PCL and A‐PEG led to A₂B₂ miktoarm star copolymer [C4S(PCL)₂‐(PEG)₂]. ¹H NMR, FT‐IR, and SEC analyses confirmed the well‐defined miktoarm star architecture. These amphiphilic miktoarm star copolymers could self‐assemble into multimorphological aggregates in water. The calix[4]arene moieties with a cavity <1 nm on the hydrophilic/hydrophobic interface of these aggregates may provide potential opportunities to entrap guest molecules for special applications in supermolecular science. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A DFT study on electronic and optical properties of aspirin-functionalized B<Subscript>12</Subscript>N<Subscript>12</Subscript> fullerene-like nanocluster

In this work, the interaction of an aspirin (AS) molecule with the external surface of a boron nitride fullerene-like nanocage (B₁₂N₁₂) is studied by means of density functional theory (DFT) calculations. Equilibrium geometry, electronic properties, adsorption energy and thermodynamic stability are identified for all of the adsorbed configurations. Four stable configurations are obtained for the interaction of AS molecule with the B₁₂N₁₂ nanocage, with adsorption energies in the range of ?10.1 to ?37.7 kcal/mol (at the M06-2X/6-31 + G** level). Our results clearly indicate that Al-doping of the B₁₂N₁₂ tends to increase the adsorption energy and thermodynamic stability of AS molecule over this nanocage. We further study the adsorption of AS over the B₁₂N₁₂ and B₁₁N₁₂Al in the presence of a protic (water) or aprotic (benzene) solvent. It is found that the calculated binding distances and adsorption energies by the PCM and CPCM solvent models are very similar, especially for the B₁₂N₁₂ complexes. According to time-dependent DFT calculations, the Al-doping can shift estimated λ _max values toward longer wavelengths (redshift). Solvent effects also have an important influence on the calculated electronic absorption spectra of AS-B₁₂N₁₂ complexes.     

The Cofactor of Tetrachloroethene Reductive Dehalogenase of Dehalospirillum multivorans Is Norpseudo‐B12, a New Type of a Natural Corrinoid

The corrinoid cofactor of the tetrachloroethene reductive dehalogenase of Dehalospirillum multivorans was isolated in its Coβ‐cyano form. This cofactor represents the main corrinoid found in D. multivorans cells. Analysis of the isolated cyano‐corrinoid by a combination of HPLC and UV/VIS‐absorbance spectroscopy revealed it to be nonidentical to a variety of known natural B₁₂ derivatives. From high‐resolution mass‐spectrometric analysis, the molecular formula of the corrinoid isolated from D. multivorans could be deduced as C₅₈H₈₁CoN₁₇O₁₄P. The sample of the novel corrinoid from D. multivorans was further analyzed by UV/VIS, CD, and one‐ and two‐dimensional ¹H‐, ¹³C‐, and ¹⁵N‐NMR spectroscopy, which indicated its structure to be closely related to that of pseudovitamin B₁₂ (Coβ‐cyano‐7″‐adeninylcobamide). By the same means, the corrinoid could be shown to differ from pseudovitamin B₁₂ only by the lack of the methyl group attached to carbon 176, and, therefore, it was named norpseudovitamin B₁₂ (or, more precisely, 176‐norpseudovitamin B₁₂). Norpseudovitamin B₁₂ represents the first example of a ‘complete’ B₁₂‐cofactor that lacks one of the methyl groups of the cobamide moiety, indicating that the B₁₂‐biosynthetic pathway in D. multivorans differs from that of other organisms. X‐Ray crystal‐structures were determined for norpseudovitamin B₁₂ from D. multivorans and the analogues pseudovitamin B₁₂ and factor A (Coβ‐cyano‐7″‐[2‐methyl]adeninylcobamide). These first accurate crystal structures of complete corrinoids with an adeninyl pseudonucleotide confirmed the expected coordination properties around Co and corroborated the close conformational similarity of the nucleotide moieties of norpseudovitamin B₁₂ and its two homologues.     

The Hydrogenobyric Acid Structure Reveals the Corrin Ligand as an Entatic State Module Empowering B12 Cofactors for Catalysis

The B₁₂ cofactors instill a natural curiosity regarding the primordial selection and evolution of their corrin ligand. Surprisingly, this important natural macrocycle has evaded molecular scrutiny, and its specific role in predisposing the incarcerated cobalt ion for organometallic catalysis has remained obscure. Herein, we report the biosynthesis of the cobalt‐free B₁₂ corrin moiety, hydrogenobyric acid ( Hby ), a compound crafted through pathway redesign. Detailed insights from single‐crystal X‐ray and solution structures of Hby have revealed a distorted helical cavity, redefining the pattern for binding cobalt ions. Consequently, the corrin ligand coordinates cobalt ions in desymmetrized “entatic” states, thereby promoting the activation of B₁₂‐cofactors for their challenging chemical transitions. The availability of Hby also provides a route to the synthesis of transition metal analogues of B₁₂.     

Study on the Interaction of Vitamin B12 with DNA by Spectroscopy and Electrochemical Methods

The Interaction between vitamin B₁₂ (VB₁₂) and fish sperm DNA was investigated in physiological buffer (pH 7.4) using the methylene blue (MB) dye as a spectral probe by spetcrophotometery, viscosity measurements and cyclic voltammetry. The apparent binding constant of vitamin B₁₂ with DNA was found to be 3.2×10⁵ mol⁻¹·L. The voltammetric behavior of vitamin B₁₂ has been investigated at glassy carbon electrode using cyclic voltammetry. Thermodynamic parameters including ΔH⁰, ΔS⁰ and ΔG⁰ for the interaction between VB₁₂ and DNA have determined as −2.3×10⁴, 27.54 and −3.1×10⁴J·mol⁻¹·K⁻¹ respectively. One indication of DNA binding mode with VB₁₂ was the change in viscosity when a small molecule associates with DNA. The diffusion coefficients of VB₁₂ in the absence (D₀)_f and presence of DNA (D₀)_b was calculated as 5.04×10⁻⁶ and 1.13×10⁻⁶ cm²·s⁻¹ respectively. The results indicated that vitamin B₁₂ can bind to DNA and the major binding mode was intercalative binding.     

Synthesis of dialkoxy- and alkoxy-amino-disubstituted derivatives of B12H12 2−

Dichloromethoxymethane reacts with the sodium salt ofcloso-dodecahydrododecaborate Na₂B₁₂H₁₂ to give disubstituted cluster, which readily decomposes when treated with various reagents. This cluster reacts with water, forming the previously described 1,7-B₁₂H₁₀(OH)_{2 2–}reaction with alcohols results in a novel 1,7-dialkoxy derivative, whereas interaction with morpholine in acetone solution affords the novel anion, 1-O-I-Prⁱ-7-O(CH₂CH₂)N-B₁₂H₁₀ ^2–. All of these derivatives were isolated as cesium salts and characterized by one- and two-dimensional NMR techniques.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 421–424, March, 1995.