Synthesis and anti-HIV evaluation of 2',3'-dideoxyribo-5-chloropyrimidine analogues: reduced toxicity of 5-chlorinated 2',3'-dideoxynucleosides

In view of the selective anti-HIV activity of 2',3'-dideoxy-3'-fluoro-5-chlorouridine (11), a series of eight 2',3'-dideoxy-5-chloropyrimidines were synthesized and evaluated for their inhibitory activity against human immunodeficiency virus type 1 (HIV-1) replication in MT-4 cells. A marked improvement in selectivity was noted for the 5-chlorouracil derivatives of 2,3-dideoxyribofuranose, 3-azido-2,3-dideoxyribofuranose, and 3-fluoro-2,3-dideoxyribofuranose, mainly due to decreased toxicity of the compounds for the host cells. While chlorination of 2',3'-dideoxycytidine removed the anti-HIV activity, introduction of a chlorine at the C-5 position of 3'-fluoro-, 3'-azido- or 2',3'-didehydro-2',3'-dideoxycytidine led to reduced cytotoxicity with only slightly reduced anti-HIV activity. X-ray analysis showed compound 11 to have two molecules in the asymmetric unit with chi = -168.8 (3) degrees and -131.3 (3) degrees and P = 179 (1) degree and 163 (1) degree, respectively; thus revealing no close resemblance to 3'-azido-3'-deoxythymidine (AZT).     

Synthesis and biological evaluation of dinucleoside methylphosphonates of 3'-azido-3'-deoxythymidine and 2', 3'-dideoxycytidine

The 5'----5' dinucleoside methylphosphonates of 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxycytidine (DDC) were prepared and evaluated for their inhibitory properties against different viruses, including human immunodeficiency virus (HIV). The synthesis of the compounds was achieved by reaction of AZT or N4-(4-monomethoxytrityl)-2',3'-dideoxycytidine with in situ prepared methylphosphonic bis (triazolide), followed in the latter case by an acidic treatment. The two title compounds showed in vitro anti-HIV activity, that was 200- to 450-fold less pronounced that that shown by the corresponding monomeric nucleosides AZT and DDC. The decreased antiviral activity may be ascribed to nuclease resistance of the methylphosphonate linkage.     

Inhibition of Mycobacterium tuberculosis, Mycobacterium bovis, and Mycobacterium avium by novel dideoxy nucleosides

The prevalence of tuberculosis (TB) and mutidrug-resistant tuberculosis (MDR-TB) has been increasing, leading to serious infections, high mortality, and a global health threat. Here, we report the identification of a novel class of dideoxy nucleosides as potent and selective inhibitors of Mycobacterium bovis, Mycobacterium tuberculosis, and drug-resistant Mycobacterium tuberculosis. A series of 5-acetylenic derivatives of 2',3'-dideoxyuridine (3-8) and 3'-fluoro-2',3'-dideoxyuridine (22-27) were synthesized and tested for their antimycobacterial activity against M. bovis, M. tuberculosis, and M. avium. 2',3'-Dideoxyuridine possessing 5-decynyl, 5-dodecynyl, 5-tridecynyl, and 5-tetradecynyl substituents (4-7) exhibited the highest antimycobacterial activity against all three mycobacteria. In contrast, in the 3'-fluoro-2',3'-dideoxyuridine series, a 5-tetradecynyl analogue (26) displayed the most potent activity against these mycobacteria. Among other derivatives, 5-bromo-2',3'-dideoxycytidine (11), 5-methyl-2',3'-dideoxycytidine (12), and 5-chloro-4-thio-2',3'-dideoxyuridine (19) exhibited modest inhibition of M. bovis and M. tuberculosis. In the series of dideoxy derivatives of adenosine, guanosine, and purines, 2-amino-6-mercaptoethyl-9-(2,3-dideoxy-beta-d-glyceropentofuranosyl)purine (32) and 2-amino-4-fluoro-7-(2,3-dideoxy-beta-d-glyceropentofuranosyl)pyrrolo[2,3-d]pyrimidine (35) were the most efficacious against M. bovis and M. tuberculosis, and M. avium, respectively.     

Structure-activity relationships of pyrimidine nucleosides as antiviral agents for human immunodeficiency virus type 1 in peripheral blood mononuclear cells

The structure-activity relationships of several pyrimidine nucleosides related to 3'-azido-3'-deoxythymidine (AZT) were determined in human immunodeficiency virus type 1 (HIV-1) infected human peripheral blood mononuclear cells. These studies indicated that nucleosides with a 3'-azido group on the sugar ring exhibited the most potent antiviral activity. Substitution at C-5 with H, CH3, and C2H5 produced derivatives with the highest potency, whereas alkyl functions greater than C2, including bromovinyl substitution reduced the antiviral potency significantly. Changing the 3'-azido function to an amino or iodo group reduced the antiviral activity. Replacement of the uracil ring by cytosine or 5-methylcytosine produced analogues with high potency and low toxicity. Modification of the 5'-hydroxy group markedly reduced the antiviral activity. Similarly, various C-nucleoside analogues related to AZT and 2',3'-dideoxycytidine were inactive and nontoxic. From these systematic studies 3'-azido-2',3'-dideoxyuridine (5a), 3'-azido-5-ethyl-2',3'-dideoxyuridine (5c), and 3'-azido-2',3'-dideoxycytidine (7a) and its 5-methyl analogue (7b) were identified as potent and selective anti-HIV-1 agent in primary human lymphocytes.     

Synthesis and antiviral activity of several 2,5'-anhydro analogues of 3'-azido-3'-deoxythymidine, 3'-azido-2',3'-dideoxyuridine, 3'-azido-2',3'-dideoxy-5-halouridines, and 3'-deoxythymidine against human immunodeficiency virus and Rauscher-murine leukemia virus

Several 2,5'-anhydro analogues of 3'-azido-3'-deoxythymidine (AZT), 3'-azido-2'3'-dideoxyuridine (AZU), 3'-azido-2'3'-dideoxy-5-bromouridine, 3'-azido-2',3'-dideoxy-5-iodouridine, and 3'-deoxythymidine and the 3'-azido derivative of 5-methyl-2'-deoxyisocytidine have been synthesized for evaluation as potential anti-HIV (human immunodeficiency virus) agents. These 2,5'-anhydro derivatives, compounds 13-17, demonstrated significant anti-HIV-1 activity with IC50 values of 0.56, 4.95, 26.5, 27.1, and 48 microM, respectively. Compared to that of the parent compounds AZT and AZU, the respective 2,5'-anhydro analogues, compounds 13 and 14, were somewhat less active. Whereas AZT was cytotoxic with a TCID50 of 29 microM, the toxicity of the 2,5'-anhydro derivative of AZT, compound 13, was reduced considerably to a TCID50 value of greater than 100 microM. The 2,5'-anhydro analogue of 5-methyl-2'-deoxyisocytidine also demonstrated anti-HIV-1 activity with an IC50 value of 12 microM. These compounds were also evaluated against Rauscher-Murine leukemia virus (R-MuLV) in cell culture. Among them, AZT, 3'-azido-2',3'-dideoxy-5-iodouridine, 3'-azido-2',3'-dideoxy-5-bromouridine, and 2,5'-anhydro-3'-azido-3'-deoxythymidine (13) were found to be most active, with IC50 values of 0.023, 0.21, 0.23, and 0.27 microM, respectively.     

Synthesis and antiretrovirus properties of 5'-isocyano-5'-deoxythymidine, 5'-isocyano-2',5'-dideoxyuridine, 3'-azido-5'-isocyano-3',5'-dideoxythymidine, and 3'-azido-5'-isocyano-2',3',5'-trideoxyuridine

The 5'-azidonucleosides 3 and 4 were obtained by treating thymidine and 2'-deoxyuridine with TPP/DEAD/HN3. The 3'-O-silylated 5'-azido-5'-deoxythymidine 5 and the corresponding 2'-deoxyuridine derivative 6 were transformed to the formamides (7 and 8, respectively) and dehydrated to the protected 5'-isocyano derivatives 9 and 10; deblocking gave 5'-isocyano-5'-deoxythymidine (11) and 5'-isocyano-2',5'-dideoxyuridine (12). 2,3'-Anhydro-5'-formamido derivatives of thymidine and 2'-deoxyuridine (19 and 20, respectively) were prepared by three different ways. In the most direct synthesis 3 and 4 were transformed to the 2,3'-anhydro-5'- azidonucleosides 17 and 18 by using TPP/DEAD; following the reaction with TPP/HCO2COCH3 gave 19 and 20. Nucleophilic opening reaction with LiN3 yielded the 3'-azido-5'-formylamino derivatives 21 and 22. Dehydration to 3'-azido-5'-isocyano-3',5'-dideoxythymidine (23) and 3'-azido-5'-isocyano-2',3',5'-trideoxyuridine (24) was achieved with tosyl chloride/pyridine. In contrast with 3'-azido-3'-deoxythymidine, compounds 11, 12, 23, and 24 were devoid of any marked inhibitory effect against DNA and RNA viruses including human immunodeficiency virus type I (HIV).     

Synthesis and in vitro evaluation of some modified 4-thiopyrimidine nucleosides for prevention or reversal of AIDS-associated neurological disorders

Oxygen-sulfur exchange at the C-4 carbonyl of several modified pyrimidine nucleosides, including 3'-azido-3'-deoxythymidine (AZT), is described in an effort to enhance the lipophilicity and, thereby, the delivery to the central nervous system of the sulfur analogues without compromising the anti-HIV activities of the parental structures. Preparation of 3'-azido-3'-deoxy-4-thiothymidine (3) proceeded from 4-thiothymidine (1) and utilized the same methodology developed for the initial synthesis of AZT. Thiation of 2',3'-didehydro-3'-deoxythymidine (4a) and 2',3'-didehydro-2',3'-dideoxyuridine (4c) was carried out with Lawesson's reagent on the corresponding 5'-O-benzoate esters, 4b and 4d, to give 5a and 5c, respectively. The latter, on alkaline hydrolysis, gave 2',3'-didehydro-3'-deoxy-4-thiothymidine (5b) and 2',3'-didehydro-2',3'-dideoxyuridine (5d), respectively. The same series of reactions were applied to the 5'-O-benzoate esters of 2',3'-dideoxyuridine (6a) and 3'-deoxythymidine (6b) to give 2',3'-dideoxy-4-thiouridine (7d) and 3'-deoxy-4-thiothymidine (7b), respectively. Characterization of the saturated and unsaturated thionucleosides included mass spectrometric studies. Under electron impact conditions, the thiated analogues gave more intense parent ions than the corresponding oxygen precursors. The lipophilicity of thymidine and the 3'-deoxythymidine derivatives are enhanced significantly, as indicated, by increases in corresponding P values (1-octanol-0.1 M sodium phosphate) upon replacement of the 4-carbonyl oxygens by sulfur. Compounds 5b, 5d, 7b, and 7d were evaluated for their effects on HIV-induced cytopathogenicity of MT-2 and CEM cells. Only 5b and 7b were moderately active in protecting both cell lines against the cytolytic effect of HIV. The inhibitory effects of analogues 5b, 5d, 7b, and 7d on thymidine phosphorylation by rabbit thymus thymidine kinase were evaluated. Only 3 showed moderate affinity (Ki = 54 microM) for the enzyme. The generally weak anti-HIV activities of the remaining thio analogues are consistent with correspondingly low susceptibilities to thymidine kinase phosphorylation as estimated from the respective Ki values of the synthetic nucleosides. However, the phosphorylation of the 5'-monophosphate derivatives to their respective 5'-triphosphates must also be considered in connection with the weak in vitro anti-HIV effects of these thiated compounds.     

Reactive 5'-substituted 2',5'-dideoxyuridine derivatives as potential inhibitors of nucleotide biosynthesis

5'-(Bromoacetamido)-2',5'-dideoxyuridine (3) and derivatives (8, 10, 12, and 14) substituted at the 5-position with bromo, iodo, fluoro, and ethyl groups have been synthesized as potential inhibitors of enzymes that metabolize pyrimidine nucleosides. Also prepared were 2',5'-dideoxyuridine derivatives (4-6) substituted at the 5'-position with 2-bromopropionamido, iodoacetamido, and 4-(fluorosulfonyl)benzamido groups. Compounds 3, 5, 8, 12, and 14 were examined for effect on macromolecular synthesis in L1210 leukemia cells in culture and compared with 5'-(bromoacetamido)-5'-deoxythymidine (1, BAT), a compound with demonstrated cytotoxicity and activity in vivo against P388 murine leukemia. Compounds 3, 8, 12, and 14 inhibited DNA synthesis without significant inhibition of RNA synthesis, and protein synthesis was affected less than DNA synthesis. Compounds 3, 5, 6, 8, 10, 12, and 14 were cytotoxic to H.Ep.-2 and L1210 cells in culture, and 3, 5, 8, and 12 showed activity in the P388 mouse leukemia screen.     

Sublethal concentrations of gemcitabine (2',2'-difluorodeoxycytidine) alter mitochondrial ultrastructure and function without reducing mitochondrial DNA content in BxPC-3 human pancreatic carcinoma cells

2',2'-Difluorodeoxycytidine (gemcitabine), a pyrimidine nucleoside analog, is used therapeutically in the treatment of pancreatic, non-small cell lung, and breast cancer. The cytotoxic effect of gemcitabine is thought to be due to masked chain termination after the triphosphorylated anabolite of the drug is incorporated into nascent DNA strands. We tested the hypothesis that sublethal concentrations of gemcitabine inhibit DNA polymerase gamma and reduce mitochondrial DNA content in BxPC-3 and MOLT-4 cell lines, and we used 2',3'-dideoxycytidine, a known inhibitor of DNA polymerase gamma as a positive control. The 6-day BxPC-3 cell growth IC(50) for gemcitabine and 2',3'-dideoxycytidine was 0.003 microM (SD +/- 0.0005) and 14.5 microM (SD +/- 4.7), respectively, and in MOLT-4 cells was 0.002 microM (SD +/- 0.001) and 0.86 muM (SD +/- 0.23), respectively. These drug concentrations were anti-proliferative but non-cytotocidal. Electron photomicrographic studies showed deranged mitochondrial cristae patterns in BxPC-3 cells treated with either gemcitabine or 2',3'-dideoxycytidine for 6 days. Mitochondrial oxidative phosphorylation dysfunction was observed as reflected by increased lactate concentration in the media of cells exposed to gemcitabine, but to a much greater extent in cells exposed to 2',3'-dideoxycytidine. PCR analysis showed that gemcitabine did not reduce mitochondrial DNA content in either BxPC-3 or MOLT-4 cells, but 2',3'-dideoxycytidine did. The effect of gemcitabine on mitochondrial ultrastructure and function did not concomitantly yield a reduction in mitochondrial DNA content. Therefore, the molecular target(s) by which gemcitabine and 2',3'-dideoxycytidine produce mitochondrial abnormalities in these cells appear to be different.     

Synthesis and anti-HIV activity of several 2'-fluoro-containing pyrimidine nucleosides

Several 2'-fluoroarabino-2',3'-dideoxy- and 2'-fluoro-2',3'-unsaturated 2',3'-dideoxy pyrimidine nucleoside analogues are reported. The saturated analogues 1-(2,3-dideoxy-2-fluoro-beta-D-threo-pentofuranosyl)thymine (2'-threo-FddT, 33), 1-(2,3-dideoxy-2-fluoro-beta-D-threo-pentofuranosyl)uracil (2'-threo-FddU, 22) were readily prepared from the corresponding 2'-deoxy-2'-fluoroarabinosyl nucleoside analogue by radical deoxygenation of the 3'-OH. The unsaturated compounds 1-(2,3-dideoxy-2-fluoro-beta-D-glycero-pent-2-enofuranosyl)thymine (2'-Fd4T, 40) and 1-[5-O-(mono-methoxytrityl)-2-fluoro-2,3-dideoxy-beta-D-glycero-pen t-2- enofuranosyl]uracil (39) were synthesized by an elimination reaction of the O-2,3'-anhydro-2'-fluoro-lyxo derivatives under basic conditions. The cytidine analogues 28 and 41 were prepared by amination of the corresponding uridine derivatives; compounds 28 and 41 were deprotected to give 1-(2,3-dideoxy-2-fluoro-beta-D-arabinofuranosyl)cytidine (2'-threo-FddC, 29) and 1-(2,3-dideoxy-2-fluoro-beta-D-glycero-pent-2- enofuranosyl)cytosine (2'-Fd4C, 42), respectively. All of these novel compounds were evaluated in vitro against human immunodeficiency virus (HIV) (LAV isolate). 2'-threo-FddC (29) was the most active of the newly synthesized substances against HIV with an ID50 of 0.8 microgram/mL; ddC had an ID50 of 0.007 micrograms/mL. Because of its potency in the initial tests, 29 was further evaluated in both T cells and macrophage/monocyte cell lines, with several different isolates of HIV. Although 2'-threo-FddC (29) exhibited good antiviral activity in these systems it was less active than AZT in these assays. At 1 microM the inhibition of CFU-GM by 29 was found to be 35-40%; this is slightly higher than seen with AZT.     

Synthesis and biological activity of various 3'-azido and 3'-amino analogues of 5-substituted pyrimidine deoxyribonucleosides

Various new 5-substituted 3'-azido- and 3'-amino derivatives of 2'-deoxyuridine and 2'-deoxycytidine have been synthesized and biologically evaluated. Among these compounds, 3'-amino-2',3'-dideoxy-5-fluorouridine (3), 3'-amino-2',3'-dideoxycytidine (7a), and 3'-amino-2',3'-dideoxy-5-fluorocytidine (7c) were found to be the most active against murine L1210 and sarcoma 180 neoplastic cells in vitro, with an ED50 of 15 and 1 microM, 0.7 and 4 microM, and 10 and 1 microM, respectively. The 3'-azido derivatives, 2 and 6c, were less active in comparison with their 3'-amino counterparts. In addition, the 5-fluoro-3'-amino nucleosides, 3 and 7c, were tested against L1210 leukemia bearing CDF1 mice. Our preliminary findings indicate that compound 7c (6 X 200 mg/kg) was as active as the positive control, 5-fluorouracil (6 X 20 mg/kg), yielding a T/C X 100 of 146 and 129, respectively. However, 3 was found to be inactive in this experiment.     

3'-Amino-2',3'-dideoxyribonucleosides of some pyrimidines: synthesis and biological activities

3'-Amino-2',3'-dideoxyribonucleosides of thymine, uracil, and 5-iodouracil (1-3) were synthesized from the corresponding 2'-deoxyribonucleosides via the threo-3'-chloro and the erythro-3'-azido derivatives. Corresponding aminonucleosides of 5-bromouracil, 5-chlorouracil, and 5-fluorouracil (4-6) were synthesized enzymatically with 3'-amino-2',3'-dideoxythymidine as the aminopentosyl donor and thymidine phosphorylase (EC 2.4.2.4) as the catalyst. 3'-Amino-2',3'-dideoxycytidine (7) was synthesized by amination of the 3'-azido precursor of 3'-amino-2',3'-dideoxyuridine. The biological activity of 3'-amino-2',3'-dideoxy-5-fluorouridine (6) was notable among this group of aminonucleosides. It had an ED50 of 10 microM against adenovirus and was not appreciably cytotoxic to mammalian cells in culture. It also had activity against some Gram-positive bacteria but not against a variety of Gram-negative bacteria. The other aminonucleosides (1-5 and 7) lacked or exhibited weak antiviral and antibacterial activities. The only compounds in this group that were appreciably toxic to mammalian cells in culture were the thymidine and deoxycytidine analogues (1 and 7).     

Synthesis and cytotoxicity of some rigid derivatives of methyl 2,5-Dihydroxycinnamate

Eight rigid compounds designed as esterase-stable analogues of methyl 2,5-dihydroxycinnamate (1) were synthesized. These derivatives include 2-(2',5'-dihydroxybenzylidene)cyclopentenone (3a), 2-(2',5'-dihydroxybenzylidene)cyclohexanone (3b), 2,6-bis(2',5'-dihydroxybenzylidene)cyclohexanone (4b), 2,6-bis(2',5'-dihydroxybenzylidene)cyclopentenone (4a), (E)-3-(2',5'-dihydroxybenzylidene)pyrrolidin-2-one (5), (E)-5-(2',5'-dihydroxybenzylidene)-1,2-isothiazolidine-1,1-dioxide (6), 4-(2',5'-dihydroxyphenyl)-5H-furan-2-one (7), and 3-(2',5'-dihydroxyphenyl)cyclopent-2-ene-1-one (8). Among the eight compounds, the furanone 7 and cyclopentenone 8 showed the most potent cytotoxicity with IC50 values of 0.39-0.98 microg/mL. Compound 8 was further brominated, phenylated and methylated at the alpha position to give three corresponding analogues, including 2-bromo-3-(2',5'-dihydroxyphenyl)cyclopent-2-ene-1-one (24), 3-(2',5'-dihydroxyphenyl)-2-phenylcyclopent-2-ene-1-one (27), and 3-(2',5'-dihydroxyphenyl)-2-methylcyclopent-2-ene-1-one (28). Among the three, the most enhanced activity was observed with the phenylated compound 27.     

Synthesis and antiviral/antitumor activities of certain 3-deazaguanine nucleosides and nucleotides

A new procedure for the preparation of the antiviral and antitumor agent 3-deazaguanine (1) and its metabolite 3-deazaguanosine (2) has been developed by reacting methyl 5(4)-(cyanomethyl) imidazole-4(5)-carboxylate (4) and 5-(cyanomethyl)-1- (2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)imidazole-4-carboxylate (6), respectively, with hydrazine. The 3-deazaguanosine 3',5'-cyclic phosphate (13) was prepared from 5-(cyanomethyl)-1-beta-D-ribofuranosyl-imidazole-4-carboxamide 5'-phosphate. Glycosylation of the trimethylsilyl 4 with 1-O-methyl-2-deoxy-3,5-di-O-p-toluoyl-D-ribofuranose in the presence of trimethylsilyl trifluoromethanesulfonate gave the corresponding N-1 and N-3 glycosyl derivatives with alpha-configuration (18 and 20) as the major products, along with minor amounts of the beta-anomers (19 and 21). However, glycosylation of the sodium salt of 4 with 1-chloro-2-deoxy-3,5-di-O-p-toluoyl-alpha-D-erythro-pentofurano se (17) gave exclusively the beta-anomers (19 and 21) in good yield. Base-catalyzed ring closure of these imidazole nucleosides gave 2'-deoxy-3-deazaguanosine (29), the alpha-anomer 28, and the corresponding N-3 positional isomers 27 and 26. The site of glycosylation and the anomeric configuration of these nucleosides have been assigned on the basis of 1' NMR and UV spectral characteristics and by single-crystal X-ray analysis for 27-29. In a preliminary screening, several of these compounds have demonstrated significant broad-spectrum antiviral activity against certain DNA and RNA viruses in vitro, as well as moderate activity against L1210 and P388 leukemia in cell culture.     

Synthesis, antiretrovirus effects, and phosphorylation kinetics of 3'-isocyano-3'-deoxythymidine and 3'-isocyano-2',3'-dideoxyuridine

The silylated AzddThd 5 and AzddUrd 6 prepared from 2,3'-anhydronucleoside derivatives 3 and 4 were transformed to formamides 7 and 8 by using the sequence RN3----RN = P(C6H5)----RNHCHO. Formamides 7 and 8 were dehydrated to the protected 3'-isocyano derivatives 9 and 10; deblocking gave 11 and 12. Neither 3'-isocyano-3'-deoxythymidine (11) nor 3'-isocyano-2',3'-dideoxyuridine (12) showed anti-HIV activity at noncytotoxic concentrations. ddThd derivative 11 was considerably more toxic to MT-4 cells than ddUrd derivative 12; it also had a much greater affinity (Ki) for MT-4 cell dThd kinase than ddUrd derivative 12. Both compounds appear to be linear mixed-type inhibitors of MT-4 cell dThd kinase.     

A novel synthesis and biological activity of several 5-halo-5'-amino analogues of deoxyribopyrimidine nucleosides

A novel synthetic procedure has been developed for the large-scale synthesis of 5-chloro-, 5-bromo-, and 5-iodo-5'-amino-2',5'-dideoxyuridine (4c-e) as well as of two new analogues, 5-iodo-5'-amino-2',5'-dideoxycytidine and 5-fluoro-5'-amino-2',5'-dideoxyuridine (4a and 4b), in good yield. The starting materials, 5-halo-2'-deoxyuridine and 5-halo-2'-deoxycytidine, are readily available and the method is straightforward. This report describes the synthesis and the biologial activities of these compounds.     

Pharmacokinetics of anti-HIV nucleosides in microswine.

The objective of the study was to determine if the micropig (Sus scrofa) would serve as an animal model for the anti-HIV nucleosides 3'-azido-3'-deoxythymidine (AZT), 2',3'-dideoxyinosine (ddI), and 2',3'-dideoxycytidine (ddC). Four adult male micropigs were administered i.v. 20 mg kg-1 AZT, 20 mg kg-1 ddI, both as 10 min infusions, and 5 mg kg-1 ddC, as an i.v. bolus. At least 12 days separated each drug administration. Following each drug administration, blood samples were collected by venipuncture and urine was collected by placement of the animals in metabolism cages. Concentrations of parent drug and AZT's glucuronide metabolite were quantitated in plasma and urine by HPLC. Data were analysed by noncompartmental methods to obtain pharmacokinetic parameters for each drug. Total and renal clearances for AZT, 0.482 +/- 0.058 and 0.326 +/- 0.075 L h-1 kg-1, respectively, and for ddI, 0.500 +/- 0.057 and 0.337 +/- 0.100 L h-1 kg-1, showed that these drugs were eliminated primarily by renal excretion rather than by liver metabolism as in man. ddC's clearances were similar to rates in man. Volume of distribution at steady state values were 0.784 +/- 0.071, 1.192 +/- 0.288 and 0.886 +/- 0.199 L kg-1 for AZT, ddI and ddC, respectively. Half-life values for AZT, ddI and ddC were 1.39 +/- 0.127, 2.585 +/- 0.243 and 1.832 +/- 0.380 h, respectively. Based on these findings, the micropig could be an appropriate model for the study of ddC in man, but not for AZT of ddI.     

Synthesis and in vitro human skin penetration of oligo- and polymeric ethylene glycol carbonates of zidovudine and stavudine

In continuation of studies focusing on the transdermal delivery of antiretroviral (ARV) drugs, the skin permeation ability of synthesized homologous series of both oligomeric and polymeric ethylene glycol (PEG) carbonates of zidovudine (3'-azido-3'-deoxythymidine, AZT, CAS 30516-87-1) and stavudine (2',3'-dideoxy-2',3'-didehydrothymine, d4T, CAS 3056-17-5) was evaluated in vitro through excised human skin in phosphate buffered solution (PBS) (0.01 M, pH 7.4) at 37 degrees C by using Franz cell diffusion methodology. The results revealed that all the derivatives permeated the skin regardless of the series. However, the derivative having three ethylene glycol repeating units was the most effective permeant in each series. The skin permeation rates of zidovudine and stavudine were enhanced by factors in the 2-4, and 1-3 range through these carbonates, respectively.