Chemistry and Bioactivity of an Artificial Adenosylpeptide B12Cofactor

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).

Resonance Raman Optical Activity Spectroscopy in Probing Structural Changes Invisible to Circular Dichroism Spectroscopy: A Study on Truncated Vitamin B12 Derivatives

This work demonstrates resonance Raman optical activity (RROA) spectra of three truncated vitamin B₁₂ derivatives modified within the nucleotide loop. Since truncated cobalamins possess sufficiently high rotational strength in the range of ROA excitation (532 nm), it was possible to record their spectra in the resonance condition. They showed several distinct spectral features allowing for the distinguishing of studied compounds, in contrast to other methods, i.e., UV-Vis absorption, electronic circular dichroism, and resonance Raman spectroscopy. The improved capacity of the RROA method is based here on the excitation of molecules via more than two electronic states, giving rise to the bisignate RROA spectrum, significantly distinct from a parent Raman spectrum. This observation is an important step in the dissemination of using RROA spectroscopy in studying the complex structure of corrinoids which may prove crucial for a better understanding of their biological role.

Does a Conjugation Site Affect Transport of Vitamin B12 -Peptide Nucleic Acid Conjugates into Bacterial Cells?

Gram-negative bacteria develop specific systems for the uptake of scarce nutrients, including vitamin B₁₂ . These uptake pathways may be utilized for the delivery of biologically relevant molecules into cells. Indeed, it was recently reported that vitamin B₁₂ transported an antisense peptide nucleic acid (PNA) into Escherichia coli and Salmonella Typhimurium cells. The present studies indicate that the conjugation site of PNA to vitamin B₁₂ has an impact on PNA transport into bacterial cells. Toward this end, a specifically designed PNA oligomer has been tethered at various positions of vitamin B₁₂ (central Co, R_5' -OH, c and e amide chains, meso position, and at the hydroxy group of cobinamide) by using known or newly developed methodologies and tested for the uptake of the synthesized conjugates by E. coli. Compounds in which the PNA oligonucleotide was anchored at the R_5' -OH position were transported more efficiently than that of other compounds tethered at the peripheral positions around the corrin ring. Of importance is the fact that, contrary to mammalian organisms, E. coli also takes up cobinamide, which is an incomplete corrinoid. This selectivity opens up ways to fight bacterial infections.

Modified vitamin B12 derivatives with a peptide backbone for biomimetic studies and medicinal applications

This short review highlights the author’s group research on modified vitamin B[Formula: see text] derivatives with a peptide backbone as (1) inhibitors of B[Formula: see text]-dependent enzymes and as (2) models of cofactor B[Formula: see text]-protein complexes.

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.

Cellular uptake of metallated cobalamins

Cellular uptake of vitamin B12-cisplatin conjugates was estimated via detection of their metal constituents (Co, Pt, and Re) by inductively coupled plasma mass spectrometry (ICP-MS). Vitamin B12 (cyano-cob(iii)alamin) and aquo-cob(iii)alamin [Cbl-OH2](+), which differ in the β-axial ligands (CN(-) and H2O, respectively), were included as control samples. The results indicated that B12 derivatives delivered cisplatin to both cellular cytosol and nuclei with an efficiency of one third compared to the uptake of free cisplatin cis-[Pt(II)Cl2(NH3)2]. In addition, uptake of charged B12 derivatives including [Cbl-OH2](+), [{Co}-CN-{cis-PtCl(NH3)2}](+), [{Re}-{Co}-CN-{cis-PtCl(NH3)2}](+), and [{Co}-CN-{trans-Pt(Cyt)(NH3)2}](2+) (Cyt = cytarabin) was high compared to neutral B12, which implied the existence of an additional internalization pathway for charged B12 vitamin analogs. The affinities of the charged B12 derivatives to the B12 transporters HC, IF and TC were similar to that of native vitamin B12.

Recent trends in the development of vitamin B12 derivatives for medicinal applications

This Feature Article highlights recent developments in the field of vitamin B12 derivatives for medicinal applications. The following topics are emphasized: (1) the development of aquacorrinoids for cyanide detection and detoxification, (2) the use of vitamin B12 conjugates and (3) antivitamins B12 for therapy and diagnosis, and (4) the design of corrinoids as activators of soluble guanylyl cyclase (sGC).

Antivitamins B12--A Structure- and Reactivity-Based Concept

B12 -antimetabolites are compounds that counteract the physiological effects of vitamin B12 and related natural cobalamins. Presented here is a structure- and reactivity-based concept of the specific 'antivitamins B12 ': it refers to analogues of vitamin B12 that display high structural similarity to the vitamin and are 'locked chemically' to prevent their metabolic conversion into the crucial organometallic B12 -cofactors. Application of antivitamins B12 to healthy laboratory animals is, thus, expected to induce symptoms of B12 -deficiency. Antivitamins B12 may, hence, be helpful in elucidating still largely puzzling pathophysiological phenomena associated with B12 -deficiency, and also in recognizing physiological roles of B12 that probably still remain to be discovered.

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 .

Incorporation of modified and artificial cofactors into naturally occurring protein scaffolds

As a possible modification of cofactor-containing proteins, cofactor-substitution typically leads to drastic changes of protein function. In particular heme, a porphyrin iron complex, is a representative, replaceable cofactor for this methodology and numerous cofactor-modified hemoproteins (reconstituted hemoproteins) have been prepared with the goal of elucidating their operational mechanism and/or engineering the protein function. In a series of hemoproteins, myoglobin, an oxygen storage hemoprotein, is one of the most rewarding scaffolds to generate a modified protein with an artificial cofactor. In this chapter, we describe practical procedures for the preparation of apomyoglobin and incorporation of zinc porphyrin as an artificial cofactor. Furthermore, we discuss the methodology to characterize the obtained cofactor-substituted proteins and the design of several artificial cofactors.

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.