Interconvertible of a vitamin B6 coenzyme analog derived from pyridoxal 5′-phosphate and rhodanine

The Z isomer of pyridoxilidenerhodanine 5'-phosphate is an efficient inhibitor of human pyridoxine 5'-phosphate oxidase, a crucial enzyme in vitamin B6 salvage pathway and a potential chemotherapeutic target

Pyridoxal 5'-phosphate (PLP), the catalytically active form of vitamin B6, acts as a cofactor in many metabolic processes. In humans, PLP is produced in the reactions catalysed by pyridox(am)ine 5'-phosphate oxidase (PNPO) and pyridoxal kinase (PDXK). Both PNPO and PDXK are involved in cancer progression of many tumours. The silencing of PNPO and PDXK encoding genes determines a strong reduction in tumour size and neoplastic cell invasiveness in models of acute myeloid leukaemia (in the case of PDXK) and ovarian and breast cancer (in the case of PNPO). In the present work, we demonstrate that pyridoxilidenerhodanine 5'-phosphate (PLP-R), a PLP analogue that has been tested by other authors on malignant cell lines reporting a reduction in proliferation, inhibits PNPO in vitro following a mixed competitive and allosteric mechanism. We also show that the unphosphorylated precursor of this inhibitor (PL-R), which has more favourable pharmacokinetic properties according to our predictions, is phosphorylated by PDXK and therefore transformed into PLP-R. On this ground, we propose the prototype of a novel prodrug-drug system as a useful starting point for the development of new, potential, antineoplastic agents.

A system of protein target sequences for anti-RNA-viral chemotherapy by a vitamin B6-derived zinc-chelating trioxa-adamantane-triol

The synthesis of the structurally unusual heterotricyclic compound 1-[3-hydroxy-5-(hydroxymethyl)-2-methyl-4-pyridinyl]-2,8,9-trioxaadamantane-3,5,7-triol (trivially named bananin, BN) from pyridoxylidenephloroglucinol and a theoretical prospect on possible biological activities of BN are presented in this report. Pyridoxylidenephloroglucinol is synthesized by Knoevenagel condensation of the vitamin B6 aldehyde pyridoxal with phloroglucinol. Pyridoxylidenephloroglucinol rearranges to light-yellow (4'RS)-1',4'-dihydrobananin by refluxing in 5M hydrochloric acid. Air oxidation subsequently forms BN in the heat which immediately yields orange-yellow (4'RS)-4'-chloro-1',4'-dihydrobananin by 1,4-addition of hydrogen chloride. This intermediate could be isolated but, interestingly, not a BN hydrochloride. Brown BN is finally achieved by base-catalyzed elimination of hydrogen chloride from (4'RS)-4'-chloro-1',4'-dihydrobananin. Regarding possible biological activities, it was demonstrated that BN acts as zinc (Zn2+) chelator. Therefore, a target of interest could be the human immunodeficiency virus type 1 (HIV-1) zinc finger HIV-1 RNA-binding nucleocapsid protein p7 (NCp7). Through suggested zinc ejection from HIV-1 genomic RNA psi-element-binding and HIV-1-RNA-duplex packaging NCp7 by BN, thus rendering NCp7 functionally obsolete, it is deduced that HIV-1 replication and effective infectious virion encapsidation could be inhibited by BN. Furthermore, theoretical and structural considerations propose that BN is converted into bananin 5'-monophosphate (BNP) by the cell type-ubiquitous human enzyme pyridoxal kinase (EC 2.7.1.35). Together with the putative antilentiviral retinoid vitamin A-vitamin B6 conjugate analogue B6RA (Kesel, A. J. Biochem. Biophys. Res. Comm. 2003, 300, 793), BNP is postulated to serve as effector in a system of protein target sequences RX(D/E) of RNA virus components. Human immunodeficiency Retroviridae (HIVs) could possibly be influenced by B6RA and BNP. In addition, candidate targets of B6RA and BNP could be adsorption, transcription and/or viral RNA replication of an interestingly wide RNA virus selection including Picornaviridae (poliovirus, human coxsackievirus, hepatitis A virus), Flaviviridae (yellow fever virus, Dengue virus, West Nile virus, Kunjin virus, St. Louis encephalitis virus, hepatitis C virus), Togaviridae (rubella virus), Coronaviridae (human coronavirus, human SARS-associated coronavirus), Rhabdoviridae (rabies virus), Paramyxoviridae (human parainfluenza virus, measles virus, human respiratory syncytial virus), Filoviridae (Marburg virus, Ebola virus), Bornaviridae (Borna disease virus), Bunyaviridae (Hantaan virus), Arenaviridae (Lassa virus), and Reoviridae (human rotavirus). The postulated scope of 'metabolically trapped' BNP might resemble the antiviral spectrum of the RNA-viral virustatic ribavirin.

Synthesis of retinoid vitamin A-vitamin B6 conjugate analogues for antiviral chemotherapy

The synthesis of retinoid vitamin A-vitamin B(6) conjugate analogues from a vitamin B(6) coenzyme analogue and putative HIV-1 trans-activating transcriptional regulatory protein Tat antagonist (Z)-5(')-O-phosphono-pyridoxylidenerhodanine (B6PR) monosodium salt hemiheptadecahydrate [(Z)-B6PRNa8.5H(2)O] is discussed here. All-trans-retinoic acid (ATRA) is coupled to B6PR by a modified Stork enamine acylation. It results in a product library of more than eight compounds, each with at least one intact all-trans or 13-cis vitamin A double bond system. This yellow oily concentrate mixture was subjected to matrix-assisted laser desorption/ionization-time-of-flight (MALDI-ToF) mass spectrometry (MS), UV/VIS-spectrophotometry, and proton nuclear magnetic resonance spectroscopy (1H-NMR). The chemical structures of six components of the concentrate mixture could be established by combination of these analytical methods. The two main components are 65% 2(')C,3O-(all-trans-retinylidyne)B6PT (B6RA) and 25% 2(')C-(all-trans-retinoyl)B6PT, chemically derived from (5RS)-5-(5(')-O-phosphono-pyridoxyl)-2,4-thiazolidinedione (B6PT). This new retinoid selection could be of further interest in antiviral applications, especially treating conditions caused by RNA viruses like HIV.

A new antioxidative vitamin B6 analogue modulates pathophysiological cell proliferation and damage

The new large scale synthesis of the yellow colored vitamin B6 analogue 5'-O-phosphono-pyridoxylidenerhodanine (2) (B6PR) leads to oligohydrates of its monosodium salt (4). The light-red hemiheptadecahydrate (8 1/2 hydrate) (4a) was crystallized and its three-dimensional structure determined by X-ray crystallography. Special nucleotide and protein interaction properties together with scavenging antioxidative function are combined in this simple water-soluble vitamin B6 analogues B6PR. High (mM) concentrations were untoxic to 'healthy' not affected cells and primary tissues. Complexation of ions (e.g. Ca2+, Fe2+, and Zn2+), modulation of nitric oxide synthases (NOS I-III), nitric oxide (NO) metabolism, and reactive oxygen species (ROS) was found. Special cytoprotecting, immunomodulating, stimulating and inhibiting activities were observed in vitro, not in comparison with some natural and synthetic pyridoxines. Low B6PR suppressed proliferation, high induced selective cell death of some cancer cell lines. Low B6PR protected HIV-1-infected CD4+ HUT 78 cells against HIV-1-mediated destruction (complete inhibition of HIV-1-induced syncytia formation and cell death) and reduced p24 level. Autoreactive S100beta-specific T cells of Lewis rat, a model of multiple sclerosis, could be influenced. Oxidative damage and age, acquired and inherited disease related pathophysiological disorders can be treated by this new cytopathology-selective versatile acting B6PR.