Potent and Selective Inhibitors of Human Immunodeficiency Virus Protease Structurally Related to L-694,746

A series of human immunodeficiency virus (HIV) protease inhibitors, which are analogues of N-[2( R)-hydroxy-1( S)-indanyl]-5( S)-[( tert-butyloxycarbonyl)amino]-4( S)-hydroxy-6-phenyl-2-( R)-[[4-(carboxymethoxy)phenyl]methyl]hexanamide (L-694,746), a metabolite of the anti-HIV agent L-689,502, were synthesized. In these compounds, the acetic group linked to the para position of the P1′ phenyl in the reference inhibitor was replaced either by the bioisosteric phosphonomethoxy group and its diisopropyl/dibenzyl derivatives, or the 1H-tetrazol-5-yl-methoxy group and its 1-benzyl derivative. In enzyme assays, phosphonomethoxy and tetrazolmethoxy analogues proved to be potent inhibitors of the HIV-1 protease, with IC50 values as low as 0.04 nM. When tested for anti-HIV-1 activity in cell-based assays, most of the new derivatives proved active, with benzyl derivatives being more active than their highly polar, unsubstituted counterparts. The dibenzylphosphonomethoxy analogue was the most active compound, with an EC50 value of 10 nM and a selectivity index of 20 000. When compounds were examined for their capability to reduce p24 levels in both acutely and chronically infected MT-4 and H9/IIIB cells, all of them were found to be active at concentrations close to those capable of preventing HIV-1-induced cytopathic effect.

8-Aza Derivatives of 3-Deazapurine Nucleosides. Synthesis and in vitro Evaluation of Antiviral and Antitumor Activity

The syntheses of 4-amino-1-(β-D-ribofuranosyl)-1 H-1,2,3-triazolo[4,5-c]pyridine (8-aza-3-deazaadenosine, 1), 4-amino-1-(2-deoxy-β-D- erythro-pentofuranosyl)-1 H-1,2,3-triazolo[4,5-c]pyridine (2′-deoxy-8-aza-3-deazaadenosine, 2), and their N8 and N7 glycosylated analogues (12,13, 21,22) and 4-amino-1-(2,3-dideoxy-β-D- erythro-pentof uranosyl)-1 H-1,2,3-triazolo [4,5-c]pyridine (2′,3′-dideoxy-8-aza-3-deazaadenosine, 3) were carried out by glycosylation of the 4-chloro-3 H-1,2,3-triazolo[4,5-c]pyridine anion. The anomeric configuration as well as the position of glycosylation were determined by 1H-, 13C-NMR, UV and N.O.E. difference spectroscopy. Nucleoside (2) and its parent compound 2′-deoxy-3-deazaadenosine were found active against ASFV and VSV. The 4-chloro-2-(β-D-ribofuranosyl)-2 H-1,2,3-triazolo[4,5-c] pyridine (9) was active against Coxsackie B1, whereas none of the 8-aza-3-deaza purine nucleosides, compound (3) included, was active against HIV-1. The 6-chloro derivatives of 8-aza-3-deazapurine ribo- and 2′-deoxyribonucleosides (11) and (20) showed some activity against LoVo human colon adenocarcinoma.

The A1 adenosine receptor as a new player in microglia physiology

The purinergic system is highly involved in the regulation of microglial physiological processes. In addition to the accepted roles for the P2 X4,7 and P2 Y12 receptors activated by adenosine triphosphate (ATP) and adenosine diphosphate, respectively, recent evidence suggests a role for the adenosine A2A receptor in microglial cytoskeletal rearrangements. However, the expression and function of adenosine A1 receptor (A1AR) in microglia is still unclear. Several reports have demonstrated possible expression of A1AR in microglia, but a new study has refuted such evidence. In this study, we investigated the presence and function of A1AR in microglia using biomolecular techniques, live microscopy, live calcium imaging, and in vivo electrophysiological approaches. The aim of this study was to clarify the expression of A1AR in microglia and to highlight its possible roles. We found that microglia express A1AR and that it is highly upregulated upon ATP treatment. Moreover, we observed that selective stimulation of A1AR inhibits the morphological activation of microglia, possibly by suppressing the Ca(2+) influx induced by ATP treatment. Finally, we recorded the spontaneous and evoked activity of spinal nociceptive-specific neuron before and after application of resting or ATP-treated microglia, with or without preincubation with a selective A1AR agonist. We found that the microglial cells, pretreated with the A1AR agonist, exhibit lower capability to facilitate the nociceptive neurons, as compared with the cells treated with ATP alone.

NMN/NaMN adenylyltransferase (NMNAT) and NAD kinase (NADK) inhibitors: chemistry and potential therapeutic applications

Nicotinamide adenine dinucleotide (NAD(+)) has a crucial role in many cellular processes, both as a coenzyme for redox reactions and as a substrate to donate ADP-ribose units. Thus, enzymes involved in NAD(+) metabolism are attractive targets for drug discovery against a variety of human diseases. Herein we focus on two of them: NMN/NaMN adenylyltransferase (NMNAT) and NAD kinase (NADK). NMNAT is a key enzyme in all organisms catalyzing coupling of ATP and NMN or NaMN yielding NAD or NaAD, respectively. NADKs are ubiquitous enzymes involved in the last step of the biosynthesis of NADP. They phosphorylate NAD to produce NADP using ATP (or inorganic polyphosphates) in the presence of Mg(2+). No other pathway of NADP biosynthesis has been found in prokaryotic or eukaryotic cells. In this review we provide a comprehensive summary of NMNAT and NADK inhibitors highlighting their chemical modifications by different synthetic approaches, and structure-activity relationships depending on their potential therapeutic applications.

Synthesis and antitumor activity of a heterodinucleotide of BVDU and gemcitabine

A heterodinucleotide comprising BVDU and Gemcitabine bound together by a 5',5'-pyrophospate bridge (BVDUp(2)dFdC) has been synthesized and evaluated as antitumor agent against AH13 rat sarcoma cells. BVDUp(2)dFdC showed a cytotoxicity similar to that of Gemcitabine.

Inhibition of HIV-1 replication in macrophages by red blood cell-mediated delivery of a heterodinucleotide of lamivudine and tenofovir

Homo- and heterodimers of nucleoside/nucleotide analogues as reverse transcriptase inhibitors are effective on HIV-1-infected human monocyte-derived macrophages (M/M) compared to the single drugs or their combination. Since the combined treatment of lamivudine (3TC) and tenofovir ((R)PMPA) has an antiretroviral efficacy and a synergic effect respect to separate drugs, the heterodinucleotide 3TCpPMPA was synthesized. A single administration of the dimer as free drug or 3TCpPMPA-loaded RBC selectively targeted to M/M was able to almost completely protect macrophages from "de novo" infection.

The antinociceptive effect of 2-chloro-2'-C-methyl-N6-cyclopentyladenosine (2'-Me-CCPA), a highly selective adenosine A1 receptor agonist, in the rat

This study was undertaken in order to investigate the effect of 2-chloro-2'-C-methyl-N(6)-cyclopentyladenosine (2'-Me-CCPA), a potent and highly selective adenosine A(1) receptor agonist, on nociceptive responses and on the ongoing or tail flick-related changes of rostral ventromedial medulla (RVM) ON- and OFF-cell activities. Systemic administrations of 2'-Me-CCPA (2.5-5 mg/kg, i.p.) reduced the nociceptive response in the plantar and formalin tests, in a way prevented by DPCPX (3 mg/kg, i.p.), a selective A(1) receptor antagonist. Similarly, intra-periaqueductal grey (PAG) 2'-Me-CCPA (0.5-1-2 nmol/rat) reduced pain behaviour in the plantar and formalin tests, in a way inhibited by DPCPX (0.5 nmol/rat). Moreover, when administered systemically (2.5-5 mg/kg, i.p.) or intra-PAG (0.5-1 nmol/rat) 2'-Me-CCPA increased the tail flick latencies, delayed the tail flick-related onset of the ON-cell burst and decreased the duration of the OFF-cell pause in a dose dependent manner. Furthermore, it decreased RVM ON-cell and increased OFF-cell ongoing activities. The in vivo electrophysiological effects were all prevented by DPCPX (0.5 nmol/rat). This study confirms the role of adenosine A(1) receptors in modulating pain and suggests a critical involvement of these receptors within PAG-RVM descending pathway for the processing of pain.

Synthesis and biological evaluation of NAD analogs as human pyridine nucleotide adenylyltransferase inhibitors

NAD analogs modified at the ribose adenylyl moiety, named N-2'-MeAD and Na-2'-MeAD, were synthesized as ligands of pyridine nucleotide (NMN/NaMN) adenylyltransferase (NMNAT). Both dinucleotides resulted selective inhibitors against human NMNAT-3 isoenzyme.

A new tiazofurin pronucleotide: synthesis and biological evaluation of cyclosaligenyl-tiazofurin monophosphate

Synthesis and biological activities of cyclosaligenyl-tiazofurin monophosphate (CycloSal-TRMP), a new tiazofurin pronucleotide, are reported. CycloSal-TRMP proved to be active in vitro against human myelogenous leukemia K562 cell line and as A1 adenosine receptor agonist.

Dinucleoside polyphosphate NAD analogs as potential NMN adenylyltransferase inhibitors. Synthesis and biological evaluation

Two dinucleoside polyphosphate NAD analogs, P1-(adenosine-5')-P3-(nicotinamide riboside-5')triphosphate (Np3A, 1) and P1-(adenosine-5')-P4-(nicotinamide riboside-5')tetraphosphate (Np4A, 2), were synthesized and tested as inhibitors of both microbial and human recombinant NMN adenylyltransferase. Compounds 1 and 2 proved to be selective inhibitors of microbial enzymes.

Erythrocyte-mediated delivery of a new homodinucleotide active against human immunodeficiency virus and herpes simplex virus

Monocyte-derived macrophages (MDMs) play a central role in the pathogenesis of infection by human immunodeficiency virus (HIV-1) and represent one of the main reservoirs of the virus in the body. In addition, MDMs can easily be infected by various herpes viruses, including herpes simplex virus type 1 (HSV-1). We have synthesized a new antiviral agent (Bis-PMEA) that consists of two 9-(2-phosphonylmethoxyethyl)adenine (PMEA) molecules bound by a phosphate bridge. This nucleotide analogue, like the parent compound PMEA, has strong and selective activity against HIV-1 and HSV-1. A drug-targeting system previously developed in our laboratory was used for the selective delivery of these drugs to macrophages. Bis-PMEA and PMEA were encapsulated into autologous erythrocytes by a procedure of hypotonic dialysis and isotonic resealing. Loaded erythrocytes were modified to increase their recognition and phagocytosis by human macrophages. By administering Bis-PMEA-loaded erythrocytes to macrophages, 47% of Bis-PMEA and 28% of PMEA was still present 10 days after phagocytosis; in contrast, only 12% of PMEA was found in macrophages receiving PMEA-loaded erythrocytes. Bis-PMEA-loaded erythrocytes were then added to macrophages infected with HIV-1 and HSV-1 and their antiviral activity evaluated. Remarkable protection was obtained against HIV-1 and HSV-1 infection (95 and 85%, respectively). Therefore, Bis-PMEA acts as an efficient antiviral prodrug that, following selective targeting to macrophages by means of loaded erythrocytes, can protect a refractory cell compartment.

Inhibition of HIV-1 replication in macrophages by red blood cell-mediated delivery of a heterodinucleotide of azidothymidine and 9-(R)-2-(phosphono methoxypropyl)adenine

Monocyte-derived macrophages (M/M) are considered important in vivo reservoirs for different kinds of viruses, including HIV. Hence, therapeutic strategies are urgently needed to protect these cells from virus infection or to control viral replication. In this paper, we report the synthesis, target delivery and in vitro efficacy of a new heterodinucleotide (AZTpPMPA), able to inhibit HIV-1 production in human macrophages. AZTpPMPA consists of two established anti-HIV drugs [zidovudine (AZT) and tenofovir (PMPA)] chemically coupled together by a phosphate bridge. This drug is not able to prevent p24 production when administered for 18 h to M/M experimentally infected with HIV-1 Bal (inhibition 27%), but can almost completely suppress virus production when given encapsulated into autologous erythrocytes (inhibition of p24 production 97%). AZTpPMPA is slowly converted to PMPA, AZT monophosphate and AZT (36 h half-life at 37 degrees C) by cell-resident enzymes. Thus AZTpPMPA should be considered a new prodrug of AZT and PMPA that is able to provide stechiometric amounts of both nucleoside analogues to macrophage cells and to overcome the low phosphorylating activity of M/M for AZT and the modest permeability of PMPA.

A new C-nucleoside analogue of tiazofurin: synthesis and biological evaluation of 2-beta-D-ribofuranosylimidazole-4-carboxamide (imidazofurin)

2-Beta-D-ribofuranosylimidazole-4-carboxamide, an imidazole analogue of the antitumor agent tiazofurin, was synthesized and evaluated for the growth inhibitory activity of human myelogenous leukemia K562 cells.

Synthesis and structure activity relationships of 5-substituted-4'-thio-beta-D-arabinofuranosylcytosines

Four 5-substituted (chloro, fluoro, bromo, methyl) 1-(4-thio-beta-D-arabinofuranosyl)cytosines and their alpha anomers were synthesized by a facile route in high yields. All of these nucleosides were evaluated for cytotoxicity against a panel of human tumor cell lines in vitro. Only 5-fluoro-1-(4-thio-beta-D-arabinofuranosyl)cytosine was found to be highly cytotoxic in all the cell lines and was further evaluated in vivo.

A new acyclic heterodinucleotide active against human immunodeficiency virus and herpes simplex virus

The most common therapies against human herpes virus (HSV-1) and human immunodeficiency virus (HIV-1) infectivity are based on the administration of nucleoside analogues. Acyclovir (ACV) is the drug of choice against HSV-1 infection, while the acyclic nucleoside phosphonate analogue PMPA has shown marked anti-HIV activity in a phase I and II clinical studies. As monocyte-derived macrophages are assumed to be important as reservoirs of both HSV-1 and HIV-1 infection, new approaches able to inhibit replication of both viruses in macrophages should be welcome. ACVpPMPA, a new heterodinucleotide consisting of both an antiherpetic and an antiretroviral drug bound by a phosphate bridge, was synthesized and encapsulated into autologous erythrocytes modified to increase their phagocytosis by human macrophages. ACVpPMPA-loaded erythrocytes provided an effective in vitro protection against both HSV-1 and HIV-1 replication in human macrophages.

C-nucleoside analogues of furanfurin as ligands to A1 adenosine receptors

Furanfurin (2-beta-D-ribofuranosylfuran-4-carboxamide) derivatives and analogues were synthesized and their affinity for adenosine receptors was determined. The agonistic behavior of furanfurin against A1 receptors is preserved only when the furan ring is substituted with isosteric pentatomic ring systems such as oxazole, thiazole or thiophene, and the carboxamide group is unsubstituted. Replacement of the hydrogen atoms of the carboxamide group with alkyl, cycloalkyl or arylalkyl groups generates compounds endowed with moderate antagonistic activity.

Synthesis, conformational analysis, and biological activity of C-thioribonucleosides related to tiazofurin

The syntheses of furanthiofurin [5beta-D-(4'-thioribofuranosyl)furan-3-carboxamide, 1] and thiophenthiofurin [5beta-D-(4'-thioribofuranosyl)thiophene-3-carboxamide, 2], two C-thioribonucleoside analogues of tiazofurin, are described. Direct trifluoroacetic acid-catalyzed C-glycosylation of ethyl furan-3-carboxylate with 1-O-acetyl-2,3,5-tri-O-benzyl-4-thio-D-ribofuranose gave 2- and 5-glycosylated regioisomers, as a mixture of alpha and beta anomers. Ethyl 5-(2,3,5-tri-O-benzyl)-beta-D-(4'-thioribofuranosyl)furan-3-carboxylate (6beta) was debenzylated and then converted into the corresponding amide (furanthiofurin) by reaction with ammonium hydroxide. A similar C-glycosylation of ethyl thiophene-3-carboxylate with 1,2,3,5-tetra-O-acetyl-4-thio-D-ribofuranose catalyzed by stannic chloride afforded an anomeric mixture of 2- and 5-glycosylated regioisomers. Deacetylation of ethyl 5-(2,3,5-tri-O-acetyl)-beta-D-(4'-thioribofuranosyl)thiophene-3-carboxylate (13beta) with methanolic ammonia and treatment of the ethyl ester with ammonium hydroxide gave thiophenthiofurin. The glycosylation site and anomeric configuration were established by (1)H NMR spectroscopy. Thiophenthiofurin was found to be cytotoxic in vitro toward human myelogenous leukemia K562, albeit 39-fold less than thiophenfurin, while furanthiofurin proved to be inactive. K562 cells incubated with thiophenthiofurin resulted in inhibition of inosine 5'-monophosphate dehydrogenase (IMPDH) and an increase in IMP pools with a concurrent decrease in GTP levels. From computational studies it was deduced that, among the C-nucleoside analogues of tiazofurin, activity requires an electrophilic sulfur adjacent to the C-glycosidic bond and an energetically favorable conformer around chi = 0 degrees. Among these, the more constrained (least flexible) compounds (tiazofurin and thiophenfurin) are more active than the less constrained thiophenthiofurin. Those compounds which contain a nucleophilic oxygen in place of the thiazole or thiophene (oxazofurin, furanfurin, and furanthiofurin) show the least activity.

Synthesis of 4'-thio-beta-D-arabinofuranosylcytosine (4'-thio-ara-C) and comparison of its anticancer activity with that of ara-C

4'-thio-beta-D-arabinofuranosylcytosine was synthesized by a facile route in high yields. It was evaluated for antitumor activity against a panel of human tumors, both in vitro and in vivo.

Synthesis and biological activity of 5-azacytosine nucleosides derived from 4-thio-2-deoxy-L-threo-pentofuranose and 4-thio-2-deoxy-D-erythro-pentofuranose

1-O-Acetyl-2-deoxy-3,5-di-O-toluoyl-4-thio-D-erythro-pentofuranose and 2-deoxy-1,3,5-tri-O-acetyl-4-thio-L-threo-pentofuranose were coupled with 5-azacytosine to obtain alpha and beta anomers of nucleosides.

Synthesis and biological application of a new heterodinucleotide with both anti-HSV and anti-HIV activity

A new antiviral drug with both anti-HSV and anti-HIV activity was synthesized by coupling Acyclovir and the acyclic nucleoside phosphonate (R)PMPA. The heterodinucleotide ACVpPMPA encapsulated into autologous erythrocytes was added to human macrophages providing an effective in vitro protection from HSV-1 and HIV-1 replication.

Potent and selective inhibitors of human immunodeficiency virus protease structurally related to L-694,746

A series of human immunodeficiency virus (HIV) protease inhibitors, which are analogues of N-[2(R)-hydroxy-1(S)- indanyl]-5(S)-[(tert-butyloxycarbonyl)amino]-4(S)-hydroxy-6-phenyl-2-(R) - [[4-(carboxymethoxy)phenyl]methyl]hexanamide (L-694,746), a metabolite of the anti-HIV agent L-689,502, were synthesized. In these compounds, the acetic group linked to the para position of the P1' phenyl in the reference inhibitor was replaced either by the bioisosteric phosphonomethoxy group and its diisopropyl/dibenzyl derivatives, or the 1H-tetrazol-5-yl-methoxy group and its 1-benzyl derivative. In enzyme assays, phosphonomethoxy and tetrazolmethoxy analogues proved to be potent inhibitors of the HIV-1 protease, with IC50 values as low as 0.04 nM. When tested for anti-HIV-1 activity in cell-based assays, most of the new derivatives proved active, with benzyl derivatives being more active than their highly polar, unsubstituted counterparts. The dibenzylphosphonomethoxy analogue was the most active compound, with an EC50 value of 10 nM and a selectivity index of 20,000. When compounds were examined for their capability to reduce p24 levels in both acutely and chronically infected MT-4 and H9/IIIB cells, all of them were found to be active at concentrations close to those capable of preventing HIV-1-induced cytopathic effect.

2'-C-Methyl analogues of selective adenosine receptor agonists: synthesis and binding studies

2'-C-Methyl analogues of selective adenosine receptor agonists such as (R)-PIA, CPA, CCPA, NECA, and IB-MECA were synthesized in order to further investigate the subdomain that binds the ribose moiety. Binding affinities of these new compounds at A1 and A2A receptors in bovine brain membranes and at A3 in rat testis membranes were determined and compared. It was found that the 2'-C-methyl modification resulted in a decrease of the affinity, particularly at A2A and A3 receptors. When such modification was combined with N6-substitutions with groups which induce high potency and selectivity at A1 receptors, the high affinity was retained and the selectivity was increased. Thus, 2-chloro-2'-C-methyl-N6-cyclopentyladenosine (2'-Me-CCPA), which displayed a Ki value of 1.8 nM at A1 receptors, was selective for A1 vs A2A and A3 receptors by 2166- and 2777-fold, respectively, resulting in one of the most potent and A1-selective agonists so far known. In functional assay, this compound inhibited forskolin-stimulated adenylyl cyclase activity with an IC50 value of 13.1 nM, acting as a full agonist.

Isosteric analogues of nicotinamide adenine dinucleotide derived from furanfurin, thiophenfurin, and selenophenfurin as mammalian inosine monophosphate dehydrogenase (type I and II) inhibitors

Dinucleotides TFAD (6), FFAD (7), and SFAD (8), isosteric NAD analogues derived, respectively, from C-nucleosides 5-beta-d-ribofuranosylthiophene-3-carboxamide (thiophenfurin, 1), 5-beta-d-ribofuranosylfuran-3-carboxamide (furanfurin, 2), and 5-beta-d-ribofuranosylselenophene-3-carboxamide (selenophenfurin, 5), were synthesized as human inosine monophosphate dehydrogenase (IMPDH) type I and II inhibitors. The synthesis was carried out by imidazole-catalyzed coupling of the 5'-monophosphate of 1, 2, and 5 with AMP. These dinucleotides, which are also analogues of thiazole-4-carboxamide adenine dinucleotide (TAD) and selenazole-4-carboxamide adenine dinucleotide (SAD), the active metabolites of the oncolytic C-nucleosides 2-beta-D-ribofuranosylthiazole-4-carboxamide (tiazofurin) and 2-beta-D-ribofuranosylselenazole-4-carboxamide (selenazofurin), were evaluated for their inhibitory potency against recombinant human IMPDH type I and II. The order of inhibitory potency found was SAD > SFAD = TFAD = TAD >> FFAD for both enzyme isoforms. No significant difference was found in inhibition of IMPDH type I and II.

Synthesis, structure, and antiproliferative activity of selenophenfurin, an inosine 5'-monophosphate dehydrogenase inhibitor analogue of selenazofurin

The synthesis and biological activity of selenophenfurin (5-beta-D-ribofuranosylselenophene-3-carboxamide, 1), the selenophene analogue of selenazofurin, are described. Glycosylation of ethyl selenophene-3-carboxylate (6) under stannic chloride-catalyzed conditions gave 2- and 5-glycosylated regioisomers, as a mixture of alpha- and beta-anomers, and the beta-2,5-diglycosylated derivative. Deprotected ethyl 5-beta-D-ribofuranosylselenophene-3-carboxylate (12 beta) was converted into selenophenfurin by ammonolysis. The structure of 12 beta was determined by 1H- and 13C-NMR, crystallographic, and computational studies. Selenophenfurin proved to be antiproliferative against a number of leukemia, lymphoma, and solid tumor cell lines at concentrations similar to those of selenazofurin but was more potent than the thiophene and thiazole analogues thiophenfurin and tiazofurin. Incubation of K562 cells with selenophenfurin resulted in inhibition of IMP dehydrogenase (IMPDH) (76%) and an increase in IMP pools (14.5-fold) with a concurrent decrease in GTP levels (58%). The results obtained confirm the hypothesis that the presence of heteroatoms such as S or Se in the heterocycle in position 2 with respect to the glycosidic bond is essential for both cytotoxicity and IMP dehydrogenase inhibitory activity in this type of C-nucleosides.

Decomposition pathways and in vitro HIV inhibitory effects of isoddA pronucleotides: toward a rational approach for intracellular delivery of nucleoside 5'-monophosphates

The decomposition pathways and kinetics in various biological media and the in vitro anti-HIV-1 and anti-HIV-2 activities of four derivatives of the 5'-mononucleotide of isoddA incorporating carboxylate esterase-labile transient phosphate protecting groups are reported and compared: namely, two mononucleoside aryl phosphoramidate derivatives 1a,b and two mononucleoside phosphotriester derivatives incorporating two S-acyl-2-thioethyl groups 2a,b. All four compounds show better antiviral activity, compared to the parent nucleoside analog isoddA. The results highlight that both types of compounds act as pronucleotides, i.e. they exert their antiviral effect via intracellular delivery of the 5'-mononucleotide of isoddA. The results may give insights for the design of new more efficient pronucleotides.

Synthesis and antiviral activity of 8-aza analogs of chiral [2-(phosphonomethoxy) propyl]guanines

(R)- And (S)-8-aza-9(-)[2-(phosphonomethoxy)propyl]guanine [(R)-and (S)-8-aza-PMPG] were synthesized and tested in vitro for anti-human immunodeficiency virus (HIV) activity. The synthesis of the above compounds and of (R)-9(-)[2-(phosphonomethoxy)propyl]guanine [(R)-PMPG] was carried out through the alkylation of 8-azaguanine or guanine with (R)- and (S)-2-O(-)[(diisopropylphosphono)methyl]-1-O-(tolylsulfonyl) -1,2-propanediol followed by deprotection of the phosphonic moiety. A different, even more convenient synthesis of (R)-8-aza-PMPG starting from 2-amino-6-chloro-5-nitro-4(3H)-pyrimidinone and (R)(-)[2(-)[(diisopropylphosphono)-methoxy]propyl]amine is also reported. Both (R)-8-aza-PMPG and (R)-PMPG demonstrated anti-HIV activity in the MTT assay with EC50 values of 12 and 4.5 microM, respectively. The corresponding S enantiomers were found to be less potent. When evaluated in combination with AZT, ddI, or DABO 603, (R)-8-aza-PMPG gave additive, additive, and synergistic anti-HIV-1 effects, respectively.

Furanfurin and thiophenfurin: two novel tiazofurin analogues. Synthesis, structure, antitumor activity, and interactions with inosine monophosphate dehydrogenase

The syntheses of furan and thiophene analogues of tiazofurin (furanfurin and thiophenfurin, respectively) are described. Direct stannic chloride-catalyzed C-glycosylation of ethyl 3-furan-carboxylate (6) or ethyl 3-thiophencarboxylate (18) with 1,2,3,5-tetra-O-acetyl-D-ribofuranose gave 2- and 5-glycosylated regioisomers, as a mixture of alpha- and beta-anomers, and the beta-2,5-diglycosylated derivatives. Deprotection of ethyl 5-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)furan-3-carboxylate (9 beta) and ethyl 5-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)thiophene-3-carboxylate (20 beta) with sodium ethoxide afforded ethyl 5-beta-D-ribofuranosylfuran-3-carboxylate (12 beta) and ethyl 5-beta-D-ribofuranosylthiophene-3-carboxylate (23 beta) which were converted into 5-beta-D-ribofuranosylfuran-3-carboxamide (furanfurin, 4) and 5-beta-D-ribofuranosylthiophene-3-carboxamide (thiophenfurin, 5) by reaction with ammonium hydroxide. The anomeric configuration and the site of glycosylation were established by 1H-NMR and proton-proton nuclear Overhauser effect difference spectroscopy. The structure of compound 23 beta was confirmed by X-ray crystallography. Thiophenfurin was found to be cytotoxic in vitro toward murine lymphocytic leukemia P388 and L1210, human myelogenous leukemia K562, human promyelocytic leukemia HL-60, human colon adenocarcinoma LoVo, and B16 melanoma at concentrations similar to that of tiazofurin. In the same test furanfurin proved to be inactive. Thiophenfurin was found active in vivo in BD2F1 mice inoculated with L1210 cells with a % T/C of 168 at 25 mg/kg. K562 cells incubation with thiophenfurin resulted in inhibition of inosine monophosphate (IMP) dehydrogenase (63%) and an increase in IMP pools (6-fold) with a concurrent decrease in GTP levels (42%). Incubation of adenosine-labeled K562 cells with tiazofurin, thiophenfurin, and furanfurin resulted in a 2-fold higher NAD analogue formulation by thiophenfurin than by tiazofurin. Furanfurin was converted to the NAD analogue with only 10% efficiency. The results obtained support the hypothesis that the presence of S in the heterocycle in position 2 with respect to the glycosidic bond is essential for the cytotoxicity and IMP dehydrogenase activity of tiazofurin, while the N atom is not.

Synthesis and evaluation of the anti-HIV activity of aza and deaza analogues of isoddA and their phosphates as prodrugs

Some aza and deaza analogues of the anti-HIV agent 2',3'-dideoxy-3'-oxoadenosine (isoddA) (8-aza-, 8-aza-1-deaza, 8-aza-3-deaza-, 1-deaza-, and 3-deaza-isoddA) were synthesized and found inactive against HIV in vitro. The hypothesis that the inactivity of these isonucleosides might be due to their poor affinity for cellular nucleoside kinases was checked by the synthesis of a series of 5'-[bis(2,2,2-trichloroethyl) phosphate] triesters and 5'-phenyl phosphoramidate derivatives which, acting as membrane soluble prodrugs, could release the free phosphate form inside the cell. The 5'-(phenylmethoxy)alaninyl phosphate derived from 8-aza-isoddA was found active against HIV-1 and HIV-2 with a potency similar to that of isoddA, while the anti-HIV potency of 5'-(phenylmethoxy)alaninyl phosphate of isoddA proved remarkably higher than that of isoddA, in particular against HIV-2, being similar to that of AZT. Further evidence that 8-aza-isoddA could behave as anti-HIV agent, provided that it is activated as phosphate, was obtained by the synthesis of its 5'-triphosphate derivative, which proved to be an active inhibitor of HIV-1 recombinant reverse transcriptase.

8-Azaxanthine derivatives as antagonists of adenosine receptors

A series of 1,3-dimethyl- and 1,3-dipropyl-8-azaxanthines, substituted at the N8 or N7 position with substituents which usually increase the affinity of the xanthines for the adenosine receptors, was synthesized and studied in radioligand binding experiments. The substitution of CH with N at the 8-position of both theophylline and caffeine dramatically reduced the affinity, as demonstrated by the fact that 8-azatheophylline and 8-azacaffeine were inert. The introduction of a methyl group at 8-position of 8-azatheophylline restored the antagonistic activity at A2 receptors, while a 8-cycloalkyl substituent increased the affinity for both receptor subtypes. A more favorable effect on affinity was produced by the substitution of the 7-methyl group in 8-azacaffeine with cycloalkyl groups. 7-Cyclopentyl-1,3-dimethyl-8-azaxanthine was 3 times more potent than caffeine at A1 receptors and 6 times less active at A2 receptors. On the contrary, the 7-cyclohexyl-1,3-dimethyl-8-azaxanthine was more potent than caffeine at A2 receptors. The substitution of 1- and 3-methyl groups with propyl in both 7- and 8-substituted 8-azatheophylline increased remarkably the affinity for A1 receptors. The 7-cyclopentyl-1,3-dipropyl-8-azaxanthine appears to be one of the most potent and selective among 7-alkyl-substituted xanthines at A1 receptors so far known. Because the 8-aza analogues of 8-substituted 1,3-dialkylxanthine were in any case less active than the corresponding xanthine derivatives, it was confirmed that the hydrogen atom at the 7-position of xanthines plays an important role in the binding to adenosine receptors.

C-glycosyl bond conformation in oxazofurin: crystallographic and computational studies of the oxazole analogue of tiazofurin

Oxazofurin is the inactive oxazole analogue of the C-glycosyl thiazole antitumor agent tiazofurin. Replacement of the thiazole sulfur in tiazofurin with the oxazole oxygen in oxazofurin produces conformational effects that are examined using crystallographic and computational methods. The crystal structure of oxazofurin contains six molecules in the asymmetric unit and has been refined to a standard R value of 6.8% for all data. The six oxazofurin conformers show an average C-glycosidic torsion angle of 70(9) degrees. This value is significantly higher than the average absolute C-glycosidic torsion angle of 24(10) degrees obtained from previous thiazole nucleoside structures. Previous studies suggest that, in tiazofurin, an electrostatic interaction between a positively charged thiazole sulfur and negatively charged furanose oxygen constrains the C-glycosidic torsion angle to a relatively small value. Ab initio molecular orbital studies presented here suggest that the higher C-glycosidic angles observed in the oxazofurin structures result from a repulsive interaction between negatively charged oxazole and furanose oxygens. Thus, it is likely that differences in activity between oxazo- and tiazofurin are either (1) due directly to differences in electronic properties between the thiazole and oxazole rings or (2) due to the variation in C-glycosidic bond conformation resulting from the alteration in the charge distribution of the heterocycle.

Synthesis and antitumor activity of 2-beta-D-ribofuranosyloxazole-4-carboxamide (oxazofurin)

Condensation of 3,4,6-tri-O-benzoyl-2,5-anhydro-D-allonyl chloride (4) with ethyl 2-amino-2-cyanoacetate (5) provided 2-[(3',4',6'-tri-O-benzoyl-2',5'-anhydroallonyl)amino]-2-cyanoa cetate (6). Compound 6 was treated with hydrogen chloride gas to give ethyl 5-amino-2-(2',3',5'-tri-O-benzoyl-beta-D- ribofuranosyl)oxazole-4-carboxylate (8). Reductive dediazotization of blocked nucleoside 8 provided ethyl 2-(2',3',5'-tri-O- benzoyl-beta-D-ribofuranosyl)oxazole-4-carboxylate (10), which after deblocking with sodium methoxide and ammonolysis was converted to 2-beta-D-ribofuranosyl-oxazole-4-carboxamide (oxazofurin, 3), an analogue of the antitumor and antiviral C-nucleoside tiazofurin (1). Oxazofurin (3) was found to be cytotoxic toward B16 murine melanoma cells in culture but inactive against murine leukemia P388 and L1210.