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.

Synthesis and biological activity of 4'-thio-L-xylofuranosyl nucleosides

A series of 4'-thio-L-xylofuranosyl nucleosides were prepared and evaluated as potential anticancer and antiviral agents. The details of a convenient and high-yielding synthesis of the carbohydrate precursor 1-O-acetyl-2,3,5-tri-O-benzyl-4-thio-L-xylofuranose (6) are presented. Proof of structure and configuration at all chiral centers of the nucleosides was obtained by proton and carbon NMR. All target compounds were evaluated in a series of human cancer cell lines in culture and as antiviral agents.

Synthesis and biological activity of 4'-thio-2'-deoxy purine nucleosides

Coupling of 1-O-acetyl-2-deoxy-3,5-di-O-toluoyl-4-thio-D-ribofuranose with 6-chloropurine and 2,6-dichloropurine gave a mixture of 9 alpha and 9 beta anomers as major products. These anomers were separated and converted to 2'-deoxy-4'-thio analogues of adenosine, inosine, guanosine, 2-amino-adenosine, and 2-chloro adenosine as well as their alpha-anomers.

Synthesis and biological activity of certain 4'-thio-D-arabinofuranosylpurine nucleosides

A series of 4'-thio-D-arabinofuranosylpurine nucleosides was prepared and evaluated as potential anticancer agents. The details of a convenient and high-yielding synthesis of the carbohydrate precursor 1-O-acetyl-2,3,5-tri-O-benzyl-4-thio-D-arabinofuranose (6) are presented. Proof of structure and configuration at all chiral centers of the nucleosides was obtained through an X-ray crystal structure of 9alpha as well as through NOE experiments on 9beta and 9alpha. All six target compounds were evaluated in a series of human cancer cell lines in culture. Two target compounds, beta anomers with diaminopurine (12) and guanine (16) as the bases, had significant cytotoxicity. One of these compounds (12) was selected for animal studies but was found to have no selectivity at the maximum tolerated dose in the murine colon 36 tumor model.

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.

Changes of plasma lipids and erythrocyte membrane fluidity in psoriatic children

Psoriasis has been associated with an abnormal plasma lipid metabolism, and changes of erythrocyte membrane lipid composition and fluidity have been shown in adult patients. To investigate whether the alterations of plasma lipids appear also in pediatric patients, we have studied plasma lipids and lipoproteins in 15 prepubertal children affected by mild-to-moderate psoriasis with respect to healthy controls. The patients showed higher levels of plasma total cholesterol (4.44 +/- 0.78 versus 4.03 +/- 0.58 mmol/L), a significant increase of cholesterol associated with HDL (1.39 +/- 0.26 versus 1.13 +/- 0.28 mmol/L, p = 0.02), and a significant decrease of the ratio LDL cholesterol to HDL cholesterol (1.73 +/- 0.6 versus 2.46 +/- 0.8, p = 0.02). By using fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene, we have shown a significant increase in fluidity in erythrocyte membrane of psoriatic children that was associated with a slight, but not significant, decrease in the cholesterol to protein ratio (422 +/- 127 versus 503 +/- 117 nmol/mg). No significant changes of phospholipid fatty acid composition have been shown, in disagreement with previous studies in adult patients. Our results support the relation between childhood psoriasis and plasma lipid changes, which are likely related to the slight compositional changes in erythrocytes. However, the observed abnormalities are expressed differently in children than in adults.

[Effect of etretinate treatment on fluidity and lipid composition of the erythrocyte membrane in patients with psoriasis]

The effect of etretinate (Ro 10-9359) treatment, at low daily dose (0.3 mg/kg), on erythrocyte membrane and physico-chemical state in psoriatic patients has been studied. The results have shown that etretinate induces a significant increase of erythrocyte membrane fluidity, as shown by a decrease of fluorescence polarization. In fact the values of 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence polarization were significantly decreased after therapy in comparison with the values observed at the beginning of the study. The modifications of membrane fluidity were associated with modifications of lipid composition. In fact the study of membrane composition has revealed a decrease of the cholesterol to protein ratio and slight but not significant changes of phospholipid fatty acid composition.