Synthesis of (6R)- and (6S)-5,10-dideazatetrahydrofolate oligo-gamma-glutamates: kinetics of multiple glutamate ligations catalyzed by folylpoly-gamma-glutamate synthetase

Folic Acid Antimetabolites (Antifolates): A Brief Review on Synthetic Strategies and Application Opportunities

Antimetabolites of folic acid represent a large group of drugs and drug candidates, including those for cancer chemotherapy. In this current review, the most common methods and approaches are presented for the synthesis of therapeutically significant antimetabolites of folic acid, which are Methotrexate (MTX), Raltitrexed (Tomudex, ZD1694), Pralatrexate, Pemetrexed, TNP-351, and Lometrexol. In addition, the applications or uses of these folic acid antimetabolites are also discussed.

Bivalent Ni(II), Co(II) and Cu(II) complexes of [(E)-[(2-methyl-1,3-thiazol-5-yl)methylidene]amino]thiourea: synthesis, spectral characterization, DNA and in-vitro anti-bacterial studies

The present work describes the preparation of bivalent Ni(II), Co(II) and Cu(II) complexes of [(E)-[(2-methyl-1,3-thiazol-5-yl)methylidene]amino]thiourea (MTHC) by mixing in 1:2 ratio of corresponding metal salt and Schiff base ligand in ethanolic medium. The prepared ligand and its complexes are confirmed using elemental analysis, magnetic moments, FT-IR, NMR, electronic and ESR spectroscopy techniques. The spectroscopic data reveals that metal complexes are in square planar in nature. In DNA binding studies, the higher intrinsic binding constants (K_b) of Ni(II), Co(II) and Cu(II) complexes are 2.713 × 10⁶ M⁻¹, 5.529 × 10⁶ M⁻¹ and 2.950 × 10⁶ M⁻¹ respectively, evident that complexes are avid binder with DNA base pairs. The moderate anti-bacterial activity (in-vitro) against staphylococcus epidermidis, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli bacterial culture may be due to the high electron density of ligand which prevents the charge reduction of metal ion. In the presence and absence of H₂O_2, it is notified that there is no appreciable DNA cleavage activity of Ni(II) and Co(II) complexes except Cu(II) complex which is due to aprotonation in the medium.

Preparation and optical parameter characterization of two aldehyde derivative thin films for photonic applications by drop casting method

In this study, thin films of polymer poly(methyl methacrylate) were prepared using a drop casting method. Two newly synthesized aldehyde derivatives, 2-bromomalonaldehyde and 5,6-dihydroimidazo[2,1-b]thiazole-2-carbaldehyde, were used at different concentrations to dope the films. The prepared films were transparent and therefore studied for application in photonics. Optical characterization of the samples was carried out using different spectroscopy techniques. Absorption spectra for both samples were obtained using a UV-vis light spectrophotometer. Other significant optical parameters, such as refractive index, extinction coefficient, and band gap energies, were calculated from the absorption spectra. The effect of doping concentration on these parameters was studied. Emission spectra were obtained using a fluorescence spectrophotometer and the effect of doping was observed. Fourier transform infrared spectra of the doped films were obtained and compared with the pure compound to note changes in peak values and peak intensity. This present work studied the effect of doping on optical properties and examined the application of the samples for photonics.

Characterisation of the bifunctional dihydrofolate synthase-folylpolyglutamate synthase from Plasmodium falciparum; a potential novel target for antimalarial antifolate inhibition

Unusually for a eukaryote, the malaria parasite Plasmodium falciparum expresses dihydrofolate synthase (DHFS) and folylpolyglutamate synthase (FPGS) as a single bifunctional protein. The two activities contribute to the essential pathway of folate biosynthesis and modification. The DHFS activity of recombinant PfDHFS–FPGS exhibited non-standard kinetics at high co-substrate (glutamate and ATP) concentrations, being partially inhibited by increasing concentrations of its principal substrate, dihydropteroate (DHP). Binding of DHP to the catalytic and inhibitory sites exhibited dissociation constants of 0.50 μM and 1.25 μM, respectively. DHFS activity measured under lower co-substrate concentrations, where data fitted the Michaelis–Menten equation, yielded apparent K_m values of 0.88 μM for DHP, 22.8 μM for ATP and 5.97 μM for glutamate. Of the substrates tested in FPGS assays, only tetrahydrofolate (THF) was efficiently converted to polyglutamylated forms, exhibiting standard kinetics with an apparent K_m of 0.96 μM; dihydrofolate, folate and the folate analogue methotrexate (MTX) were negligibly processed, emphasising the importance of the oxidation state of the pterin moiety. Moreover, MTX inhibited neither DHFS nor FPGS, even at high concentrations. Conversely, two phosphinate analogues of 7,8-dihydrofolate that mimic tetrahedral intermediates formed during DHFS- and FPGS-catalysed glutamylation were powerfully inhibitory. The K_i value of an aryl phosphinate analogue against DHFS was 0.14 μM and for an alkyl phosphinate against FPGS 0.091 μM, with each inhibitor showing a high degree of specificity. This, combined with the absence of DHFS activity in humans, suggests PfDHFS–FPGS might represent a potential new drug target in the previously validated folate pathway of P. falciparum.

Inhibition of human folylpolyglutamate synthetase by diastereomeric phosphinic acid mimics of the tetrahedral intermediate

Phosphorus-containing pseudopeptides, racemic at the C-terminal alpha-carbon, are potent mechanism-based inhibitors of folylpolyglutamate synthetase (FPGS). They are mimics of the tetrahedral intermediate postulated to form during FPGS-catalyzed biosynthesis of poly(gamma-l-glutamates). In the present paper, the FPGS inhibitory activity of each diastereomer coupled to three heterocycles is reported. The high R(f) pseudopeptide containing the 5,10-dideazatetrahydropteroyl (DDAH(4)Pte) heterocycle is most potent (K(is) = 1.7 nM). While the heterocyclic portion affects absolute FPGS inhibitory potency, the high R(f) species is more potent in each pair containing the same heterocycle. This species presumably has the same stereochemistry as the natural folate polyglutamate, i.e., (l-Glu-gamma-l-Glu). Unexpectedly, the low R(f) (presumed l-Glu-gamma-d-Glu) species are only slightly less potent (<30-fold) than their diastereomers. Further study of this phenomenon comparing l-Glu-gamma-l-Glu and l-Glu-gamma-d-Glu dipeptide-containing FPGS substrates shows that <1% contamination of commercial d-Glu precursors by l-Glu may give misleading information if l-Glu-gamma-l-Glu substrates have low K(m) values.

Concentration-dependent processivity of multiple glutamate ligations catalyzed by folylpoly-gamma-glutamate synthetase

Folylpoly-gamma-glutamate synthetase (FPGS, EC 6.3.2.17) is an ATP-dependent ligase that catalyzes formation of poly-gamma-glutamate derivatives of reduced folates and antifolates such as methotrexate and 5,10-dideaza-5,6,7,8-tetrahydrofolate (DDAH 4PteGlu 1). While the chemical mechanism of the reaction catalyzed by FPGS is known, it is unknown whether single or multiple glutamate residues are added following each folate binding event. A very sensitive high-performance liquid chromatography method has been used to analyze the multiple ligation reactions onto radiolabeled DDAH 4PteGlu 1 catalyzed by FPGS to distinguish between distributive or processive mechanisms of catalysis. Reaction time courses, substrate trapping, and pulse-chase experiments were used to assess folate release during multiple glutamate additions. Together, the results of these experiments indicate that hFPGS can catalyze the processive addition of approximately four glutamate residues to DDAH 4PteGlu 1. The degree of processivity was determined to be dependent on the concentration of the folate substrate, thus suggesting a mechanism for the regulation of folate polyglutamate synthesis in cells.

Prodrug forms of N-[(4-deoxy-4-amino-10-methyl)pteroyl]glutamate-gamma-[psiP(O)(OH)]-glutarate, a potent inhibitor of folylpoly-gamma-glutamate synthetase: synthesis and hydrolytic stability

Ester prodrugs of the phosphinate pseudopeptide N-[(4-deoxy-4-amino-10-methyl)pteroyl]glutamate-gamma-[psiP(O)(OH)]-glutarate (1a) were synthesized. H-phosphinic acids derived from N-Cbz vinyl glycine esters were converted to the desired pseudopeptides by Michael addition to alpha-methyleneglutarate esters. Pivaloyloxymethyl (POM) ester moieties were incorporated in both the N-terminal and C-terminal fragments prior to formation of either C-P bond. N-Alkylation of the corresponding amides derived from p-(N-methyl)aminobenzoic acid with 2,4-diamino-6-(bromomethyl)pteridine gave the target compounds. POM esters of methotrexate and the corresponding gamma-glutamyl conjugate were also synthesized using the same strategy. All prodrugs were evaluated in Chinese hamster ovary cells. Although the pseudopeptide prodrugs were ineffective, prodrugs of methotrexate and the corresponding gamma-glutamyl conjugate were equipotent with the parent compounds. Stability of the prodrugs was investigated in both phosphate buffer and cell line medium to provide a rationale for the observed biological data.