Conjugation of phosphonoacetic acid to nucleobase promotes a mechanism-based inhibition

Small molecule inhibitors have a powerful blocking action on viral polymerases. The bioavailability of the inhibitor, nevertheless, often raise a significant selectivity constraint and may substantially limit the efficacy of therapy. Phosphonoacetic acid has long been known to possess a restricted potential to block DNA biosynthesis. In order to achieve a better affinity, this compound has been linked with natural nucleotide at different positions. The structural context of the resulted conjugates has been found to be crucial for the acquisition by DNA polymerases. We show that nucleobase-conjugated phosphonoacetic acid is being accepted, but this alters the processivity of DNA polymerases. The data presented here not only provide a mechanistic rationale for a switch in the mode of DNA synthesis, but also highlight the nucleobase-targeted nucleotide functionalization as a route for enhancing the specificity of small molecule inhibitors.     

Synthesis and Substrate Properties of Modified Nucleoside 5"-Triphosphates Mimicking dATP in the Reactions of DNA Synthesis Catalyzed by DNA Polymerases

Several modified nucleoside 5"-triphosphates containing adenine-mimicking pyrimidine derivatives as an aglycone were synthesized. The study of substrate properties of these compounds towards DNA-synthesizing enzymes showed their ability of being incorporated into the growing DNA chain in place of dATP.     

Synthesis of Novel Difluoro-Cyclopropyl Guanine Nucleosides and Their Phosphonate Analogues as Potent Antiviral Agents

The synthesis of new rigid guanine analogues with anti-HIV-1 and anti-herpes viral activities is described. The phosphonate of difluorocyclopropane nucleoside analogue 26 exhibits in vitro anti-HIV-1 activity similar to that of PMEA in MT-4 cells. Further, analogue 20 shows moderate anti-HCMV activity in MRC cells.     

Adenosine Analogues as Inhibitors or Inactivators of S-Adenosylhomocysteine Hydrolase from Bovine Pancreas

Abstract

The ability of some substrate-analogues to inhibit or to inactivate S-adenosylhomocysteine hydrolase (SAHase) purified from bovine pancreas was investigated. Our results confirm that 3-deazaarysteromicin (DZAry) is a more potent competitive inhibitor than 3-deazaadenosine (DZA), while nebularine (purine riboside), contrary to previous reports, showed an uncompetitive inhibition. Moreover, 2-chloroadenosine and 2′-deoxyadenosine were found to be irreversible inactivators of SAHase with increasing potency, respectively. K_i values found for these drugs were of the same order of magnitude as those reported for SAHases from other mammalian tissues. The SAHase substrate-analogues studied are believed to act as antineoplastic and/or antiviral agents. It is conceivable to postulate that their therapeutic effects could be, at least in part, attributable to inhibition or even to inactivation of SAHase which, in turn, causes a reduction in S-adenosylmethionine-dependent methylation reactions.     

The Reaction Mechanism of Pyrimidine Nucleoside Synthesis by the Nitromethane Mercuric Cyanide Method

8,4?-dieckol is a natural product which has been isolated from brown alga, Ecklonia cava. This polyphenolic compound is a phlorotannin derivative with a broad range of bioactivities. Its inhibitory activity on human immunodeficiency virus type-1 (HIV-1) was tested and the results indicated that 8,4?-dieckol inhibited HIV-1 induced syncytia formation, lytic effects, and viral p24 antigen production at noncytotoxic concentrations. Furthermore, it was found that 8,4?-dieckol selectively inhibited the activity of HIV-1 reverse trancriptase (RT) enzyme with 91% inhibition ratio at the concentration of 50?μM. HIV-1 entry was also inhibited by 8,4?-dieckol. According to data from this study, 8,4?-dieckol is an effective compound against HIV-1 with high potential for further studies. These results suggest that it might be used as a drug candidate for the development of new generation therapeutic agents, although further studies on the mechanism of inhibition should be addressed.     

Synthesis and Evaluation of 6‐Aza‐2′‐deoxyuridine Monophosphate Analogs as Inhibitors of Thymidylate Synthases,and as Substrates or Inhibitors of Thymidine Monophosphate Kinase in Mycobacterium tuberculosis

A series of 5‐substituted analogs of 6‐aza‐2′‐deoxyuridine 5′‐monophosphate, 6‐aza‐dUMP, has been synthesized and evaluated as potential inhibitors of the two mycobacterial thymidylate synthases (i.e., a flavin‐dependent thymidylate synthase, ThyX, and a classical thymidylate synthase, ThyA). Replacement of C(6) of the natural substrate dUMP by a N‐atom in 6‐aza‐dUMP 1a led to a derivative with weak ThyX inhibitory activity (33% inhibition at 50 μM ). Introduction of alkyl and aryl groups at C(5) of 1a resulted in complete loss of inhibitory activity, whereas the attachment of a 3‐(octanamido)prop‐1‐ynyl side chain in derivative 3 retained the weak level of mycobacterial ThyX inhibition (40% inhibition at 50 μM ). None of the synthesized derivatives displayed any significant inhibitory activity against mycobacterial ThyA. The compounds have also been evaluated as potential inhibitors of mycobacterial thymidine monophosphate kinase (TMPKmt). None of the derivatives showed any significant TMPKmt inhibition. However, replacement of C(6) of the natural substrate (dTMP) by a N‐atom furnished 6‐aza‐dTMP ( 1b ), which still was recognized as a substrate by TMPKmt.     

4,5,6‐Trisubstituted Piperidinones as Conformationally Restricted Ceramide Analogues: Synthesis and Evaluation as Inhibitors of Sphingosine and Ceramide Kinases and as NKT Cell‐Stimulatory Antigens

The conformationally based piperidinone sphingosine analogues 7, 8, 15 , and 16 were synthesized from allylic alcohol 34 via lactams 31 and 32 . The l‐ arabino diol 7 and the l‐ ribo diol 8 were transformed into the amino alcohols 17 – 24 . The l‐ gluco ceramide analogues 43, 46a , and 47 , and the l‐ altro ceramide analogues 51a and 52 were synthesized from either 31 or 32 . The l‐ ribo diols 8 and 16 , and the amino alcohols 19 and 20 inhibit sphingosine kinase 1 (SPHK1), while the l‐ arabino analogues 7, 15, 17 , and 18 are inactive. The l‐ arabino and the l‐ ribo dimethylamines 21 – 24 , the l‐ gluco ceramide analogues 43, 46a , and 47 , and the l‐ altro ceramide analogues 51a and 52 did not block SPHK1. Neither the l‐ arabino diol 7 nor the l‐ ribo diol 8 inhibited SPHK2 or ceramide kinase. The l‐ arabino diols 7 and 15 stimulate invariant natural killer T (iNKT) cells when presented by living antigen‐presenting cells (APC) and also by plate‐bound human CD1d, whereas the l‐ ribo diols 8 and 16 , the l‐ arabino amino alcohols 17 – 18 , and the dimethylamines 21 – 22 did not activate iNKT cells. The l‐ gluco ceramide analogues 43, 46a , and 47 had strongly stimulatory effects on iNKT cells when presented by living APC and also by plate‐bound human CD1d, whereas the l‐ altro ceramide analogue 52 activated only weakly. All activatory compounds induced preferentially the release of pro‐inflammatory cytokines, indicating the formation of a stable CD1d? lipid? T‐cell receptor complex.     

Repair of DNA damage induced by methylating agents in human uterine cervical cells with or without cancer precursor lesions

Experiments were carried out to study the repair capabilities of normal human cervical fibroblasts and fibroblasts derived from human uterine cervical dysplasia, carcinoma in situ and invasive carcinoma. Sedimentation analysis of DNA in alkaline sucrose density gradient was carried out to monitor the DNA damage induced by a methylating carcinogen, methylnitrosourea (MNU). The results indicate that none of the cell lines, namely, fibroblasts either derived from normal human uterine cervix (T₃₀-11) or from cervical cells of cancer precursor lesions (T₄-3F; T₂₃-3; T₁₈) exhibited any significant repair in 72 h. In contrast fibroblasts derived from normal human skin (GM105) exhibited 38% repair of their DNA damaged by MNU. Epithelial-like cells (T₄-3E) obtained from cervical dysplasia exhibited only 18% repair of MNU-induced DNA damage in 72 h.When the damage was induced by another methylating agent, methyl methanesulfonate (MMS), fibroblasts from normal human skin (GM105) exhibited 40% repair of the damaged DNA whereas fibroblasts from normal human uterine cervix (T₃₀-11) exhibited only a 16% repair, in 72 h.These results suggest that fibroblasts derived from either normal human uterine cervix or from cervix with cancer precursor or cancer lesions exhibit low levels of repair of DNA damged by methylating agents.     

Synthesis and evaluation of 1,2,3,4-tetrahydro-1-acridone analogues as potential dual inhibitors for amyloid-beta and tau aggregation

Amyloid-β (Aβ) and tau protein are two crucial hallmarks in Alzheimer’s disease (AD). Their aggregation forms are thought to be toxic to the neurons in the brain. A series of new 1,2,3,4-tetrahydro-1-acridone analogues were designed, synthesized, and evaluated as potential dual inhibitors for Aβ and tau aggregation. In vitro studies showed that compounds 25–30 (20?μM) with N-methylation of the quinolone ring effectively inhibited Aβ_1-42 aggregation by 84.7%–99.5% and tau aggregation by 71.2%–101.8%. Their structure-activity relationships are discussed. In particular, 30 could permeate the blood-brain barrier, bind to Aβ_1-42 and tau, inhibit Aβ_1-42 β-sheets formation, and prevent tau aggregation in living cells.