A series of polyhydroxylated 2-phenylbenzothiazoles 3 has been prepared by demethylation of the precursor methoxylated 2-phenylbenzothiazoles 9. The key step in the construction of the benzothiazole nucleus involves a Jacobson cyclization of methoxylated thiobenzanilides 8. The target compounds inhibit WiDr human colon tumor cells and MCF-7 human mammary tumor cells in vitro with IC50 values in the low micromolar range, but the activity against MCF-7 cells is not related to estrogen receptor-binding affinity. None of the compounds showed selective cytotoxicity against Abelson virus-transformed ANN-1 cells encoded with the pp120gag-abl tyrosine kinase compared with the parental 3T3 line. Compounds were only marginally inhibitory to the EGF receptor-associated protein tyrosine kinase from a membrane preparation of A431 cells. The most active compound was 4,6-dihydroxy-2-(4-hydroxyphenyl)benzothiazole (3b) which has the same overall hydroxyl substitution pattern as genistein (1a). The compounds were weakly cytotoxic for an EGF receptor, overexpressing cell line HN5, but when tested for differential toxicity against the EGF receptor tyrosine kinase or the PDGF receptor tyrosine kinase in a standard mitogenesis assay utilizing human fibroblasts, no discrimination was observed. In this assay, the compounds inhibited DNA synthesis when added to cells during S phase. This suggests that inhibition could not be interpreted in terms of tyrosine kinase inactivation but more likely as a relatively broad specificity for the ATP-binding domain of other kinases such as thymidine kinase.

No abstract

This review regards various attitudes to the rational design of prodrugs derived of nucleoside and nucleotide analogues with pronounced biological (antiviral, anticancer) activity. Particular attention is focused on the recent development of prodrugs of approved therapeutic agents with the above structural association.

Pyranosyl nucleotide analogues have been designed so that the intramolecular base to phosphorus distance closely approximates that of natural nucleotides. This was achieved by attaching the phosphorus directly at the anomeric position and the base at the 4-position of the carbohydrate. A series of compounds incorporating natural bases and having this novel structure were made via a short synthesis starting from commercially available glycals. Addition of triisopropyl phosphite to the glycals furnished alpha- and beta-2-enopyranosylphosphonates which were then substituted with the heterocycle using Mitsunobu chemistry. Deprotection afforded the 2',3'-unsaturated isonucleotide analogue. In some cases the deprotection sequence induced double-bond migration leading to the 1',2'-unsaturated derivative. NMR spectroscopic structural analysis established an axial preference for the base and an equatorial preference for the beta-phosphorus which results in intramolecular base to phosphorus distances within 1 A of that of natural nucleotides. All of the deprotected compounds were screened for inhibition of HCMV, HSV-2, and HIV replication. Several compounds inhibited HCMV and HSV-2, the most potent of which was the unsaturated cytosine analogue 18 (HCMV IC50 = 10 microM, HSV-2 IC50 = 85 microM). None of the compounds were cytotoxic at the highest dose (1 mM) tested. None of the compounds were inhibitory to HIV.

Reaction of (R)-1-O-p-toluenesulfonyl-1,2,3-propanetriol (IV) with N-trimethylacetylimidazole (II) afforded (R)-1-O-p-toluenesulfonyl-3-O-trimethyacetyl-1,2,3-propanetriol (V) which was reacted with dimethoxymethane in the presence of phosphorus pentoxide to give (R)-2-O-methoxymethyl-1-O-p-toluenesulfonyl-3-O-trimethyacetyl-1,2,3-propanetriol (VI). Compound VI was treated with acetic anhydride and boron trifluoride etherate and the obtained 2-acetoxy derivative VII reacted with bromotrimethylsilane to give the intermediary bromomethyl ether VIII. Compound VIII on reaction with tris(2-propyl) phosphite afforded (R)-2-O-bis(2-propyl)phosphonomethyl-1-O-p-toluenesulfonyl-3-O-trimethyacetyl-1,2,3-propanetriol (IX). Condensation of synthon IX with sodium salts of adenine, 2,6-diaminopurine, or with cytosine, 6-azacytosine or 2-chloroadenine in the presence of cesium carbonate, afforded fully protected diesters X and XIIIb which on methanolysis and reaction with bromotrimethylsilane gave N-[(S)-(3-hydroxy-2-phosphonomethoxypropyl)] derivatives of adenine (XIa), 2- chloroadenine (XIb), 2,6-diaminopurine (XIc), cytosine (XIVa) and 6-azacytosine (XIVb). In an analogous reaction, sodium salt of 4-methoxy-2-pyrimidone reacted with compound IX to give an intermediate XIIIa which on treatment with methanolic ammonia and subsequent deblocking under the same conditions also afforded the cytosine derivative XIVa. Sodium salt of 2-amino-6-chloropurine was in this way converted into the corresponding 2-aminopurine derivative XVIII. Deprotection of this compound gave 9-(S)-(3-hydroxy-2-phosphonomethoxypropyl)-2-aminopurine (XIX).