A. Stanley Jones

Synthesis of some 5-halogenovinyl derivatives of uracil and their conversion into 2′-deoxyribonucleosides

Treatment of 5-formyluracil with malonic acid in the presence of piperidine gave (E)-5-(2-carboxyvinyl)uracil which, upon reaction with the appropriate N-halogenosuccinimide, gave (E)-5-(2-bromovinyl)uracil, (E)-5-(2-chlorovinyl)uracil, and (E)-5-(2-iodovinyl)uracil. The last mentioned compound was also obtained by the action of iodine chloride on 5-vinyluracil. 5-(1-Chlorovinyl)uracil upon treatment with bromine gave 5(2-bromo-1-chlorovinyl)uracil which reacted with sodium methoxide to give 5-bromoethynyluracil. (E)-5-(2-Bromovinyl)-uracil was converted into into its trimethylsilyl derivative which was condensed with 2-deoxy-3,5-di-O-(p-toluoyl)-α-D-erythro-pentofuranosyl chloride to give the α- and β-anomers of the blocked deoxyribonucleoside. Removal of the p-toluoyl blocking groups with sodium methoxide afforded (E)-5-(2-bromovinyl)-1-(2-deoxy-α-D-erythro-pentofuranosyl)uracil and (E)-5-(2-bromovinyl)-2′-deoxyuridine. A similar series of reactions gave (E)-5-(2-iodovinyl)-2′-deoxyuridine and 5-(2-bromo-1-chlorovinyl)-2′-deoxyuridine. 5-(1-Chlorovinyl)uracil could be condensed similarly with the blocked sugar derivative to give the α- and β-anomers of the blocked deoxyribonucleoside. Attempted removal of the groups with sodium methoxide gave 2′-deoxy-5-ethynyluridine and mild treatment with methanolic ammonia gave the same product and some 2′-deoxy-5-ethynyl-5′-O-(p-toluoyl)-uridine. 5-(1-Chlorovinyl)-2′-deoxyuridine was obtained by the addition of HCl to 2′-deoxy-5-ethynyluridine. Aspects of the elimination reactions of 5-(halogenovinyl)uracil derivatives are discussed.

Synthesis, properties and biological activity of some nucleoside cyclic phosphoramidates

Reaction of the appropriate nucleoside with phosphoryl trichloride and then with N-methylethanolamine gave 2′,3′-O-isopropylidene-5′-O-(3″-methyl-1″-oxa-3″-aza-2″-phosphacyclopentan-2″-yl)uridine 2″-oxide (4), 5′-O-(3″-methyl-1″-oxa-3″-aza-2″-phosphacyclopentan-2″-yl)thymidine 2″-oxide (5), and 2′-deoxy-5-fluoro-5′-O-(3″-methyl-1″-oxa-3″-aza-2″-phosphacyclopentan-2″-yl)uridine 2″-oxide (6). A similar sequence of reactions, but using N,N′-dimethylethylenediamine, gave 5′-O-(1″,3″-dimethyl-1″,3″-diaza-2″-phosphacyclopentan-2″-yl)thymidine 2″-oxide (7) and 2′-deoxy-5′-O-(1″,3″-dimethyl-1″,3″-diaza-2″-phosphacyclopentan-2″-yl)-5-fluorouridine 2″-oxide (8).Compounds (4)–(8) were hydrolysed readily in the pH range 6.0–7.0 at 25 °C, the kinetics being first order in hydrogen ions and in substrate. The 1-oxa-3-aza-2-phospha derivatives were hydrolysed more readily than the 1,3-diaza-2-phospha derivatives and the 2′-deoxy-5-fluorouridine derivatives more rapidly than the thymidine derivatives. In each case hydrolysis resulted in the fission of one P–N bond.Compound (8) inhibited the growth of leukemia L1210 cells. It acted as a thymidylate synthetase inhibitor in the cell culture, but itself was not a substrate for the isolated, purified enzyme.

Synthetic analogues of polynucleotides. Part XII. Synthesis of thymidine derivatives containing an oxyacetamido- or an oxyformamido-linkage instead of a phosphodiester group

The dinucleotide analogue thymidinylacetamido-[3′(O)→ 5′(C)]-5′-deoxythymidine was synthesised. The compound showed a hypochromic effect of about 10% at 268 nm. At pH 6·0–7·5 and 20° the compound was stable; in M-sodium hydroxide at 37° it was 50% hydrolysed after 3·4 h. 5′-Azido-5′-deoxythymidine was converted into its 3′-O-carboxymethyl derivative and this was reduced to give 5′-amino-3′-O-carboxymethyl-5′-deoxythymidine. Attempts to polymerise this compound were unsuccessful because of the ready formation of a lactam. Thymidinylformamido-[3′(O)→ 5′(C)]-5′-deoxythymidine was also synthesised. It showed a hypochromic effect of about 8% at 267 nm and was more stable to alkali than the acetamido-compound.

Synthesis of some nucleoside cyclic phosphoramidates and related compounds via phosphoramidites

Reaction of 2-chloro-3-methyl-1-oxa-3-aza-2-phosphacyclopentane with thymidine and with 2′-deoxy-5-fluorouridine gave their 3′,5′-bis-O-(3-methyl-1-oxa-3-aza-2-phosphacyclopentan-2-yl) derivatives (5) and (6). Reaction of these nucleosides with 2-chloro-1,3-dimethyl-1,3-diaza-2-phosphacyclopentane gave 3′,5′-bis-O-(1,3-dimethyl-1,3-diaza-2-phosphacyclopentan-2-yl) derivatives (7) and (8). The phosphoramidites, (7) and (8) were oxidised with dinitrogen tetraoxide to the corresponding phosphoramidates (9) and (10). Attempts to oxidise (5) and (6) in a similar way resulted in opening of the phosphoramidate ring. Treatment of compounds (5)–(8) with sulphur gave the corresponding phosphorothioamidates (11)–(14). The hydrolysis of 3′,5′-bis-O-(1,3-dimethyl-2-oxo-1,3-diaza-2-phosphacyclopentan-2-yl)thymidine (9) was studied using 31P n.m.r. spectroscopy. At pH 7.0 and 25 °C the half-life was 21 h. Both phosphorus heterocyclic rings opened at the same rate. The hydrolysis of the second ring proceeded at ca. three times the rate of hydrolysis of the first. 2′-Deoxy-5-fluoro-3′,5′-bis-O-(1,3-dimethyl-2-oxo-1,3-diaza-2-phosphacyclopentan-2-yl)-uridine (10) did not inhibit isolated purified thymidylate synthetase and was only a weak inhibitor of leukemia L1210 cell growth.

A simple method for the preparation of ‘ribonucleoside dialdehydes’ and some comments on their structure

Adenosine, guanosine, inosine, cytidine, and uridine have been oxidised with periodate to give the respective α-substituted derivatives of α′-hydroxymethyloxydiacetaldehyde (‘ribonucleoside dialdehydes’). These have been isolated by a simple procedure which involves extraction with ethanol, thus separating the dialdehydes from inorganic material. The compounds so isolated are more stable than has been suggested by early work in this field. I.r. and n.m.r. spectroscopy show that the compounds contain few if any free aldehyde groups. They appear to be mixtures of hydrated forms although they run as single spots on t.l.c. in several solvent systems. Dried samples also contain virtually no aldehyde groups, and the possibility that they are polymeric structures as suggested by others, is discussed. With the exception of ‘guanosine dialdehyde,’ the amplitude of the Cotton effect in the o.r.d. spectrum is less than that in the parent ribonucleoside.

The synthesis of nucleosides derived from 5-ethynyluracil and 5-ethynylcytosine

5-Ethynyluridine and 2′-deoxy-5-ethynyluridine have been synthesised by condensation of the trimethylsilyl derivative of 5-ethynyluracil with the appropriate blocked sugar derivatives and removal of the blocking groups. The α-anomer of 2′-deoxy-5-ethynyluridine was also obtained. 2,4-Dichloro-5-(1-chlorovinyl)pyrimidine upon treatment with ammonia gave a mixture of 2-amino-4-chloro-5-(1-chlorovinyl)pyrimidine and 4-amino-2-chloro-5-(1-chlorovinyl)pyrimidine. The latter upon treatment with potassium hydroxide in aqueous dioxan gave 5-ethynylcytosine. Condensation of the trimethylsilyl derivative of 5-ethynylcytosine with appropriate protected sugar derivatives and removal of the protecting groups gave 5-ethynylcytidine, 2′-deoxy-5-ethynylcytidine, and its α-anomer.

Migration and stability of the silyl group in the use of phenylthiomethyltrimethylsilane as a formyl synthon

Abstract 1,4-Silyl group migration from the oxygen in the reaction between phenylthiomethyl-trimethylsilane and epibromohydrin is reported.

Some chemical reactions of 5-vinyluracil and 2′-deoxy-5-vinyluridine

In an attempt to elucidate the chemical reactions responsible for the antiviral and toxic properties of 2′-deoxy-5-vinyluridine (1), the chemistry of some 5-vinyluracil derivatives has been studied. Under aqueous acidic conditions 5-vinyluracil (5) is in equilibrium with 5-(1 -hydroxyethyl)uracil (6) and the dimer, (E)-1,3-bis(uracil-5-yl)but-1-ene (9). The formation of (9) is favoured in concentrated solution. Upon treatment with aqueous acid compound (1) gives 2′-deoxy-5-(1-hydroxyethyl)uridine (4) but no dimerisation occurs. 1-Ethyl-5-vinyluracil (7) has been synthesized and this in hydrochloric acid gives the dimer, (E)-1,3-bis(1-ethyluracil-5-yl)but-1-ene (10). Under similar conditions compound (5) reacts with L-cysteine to give 5-(1-L-cystein-S-ylethyl)uracil (11) and with phenol to give a mixture of substituted phenols. Compound (1) reacts with butan-1-ol in the presence of trifluoroacetic acid to give 5-(1-butoxyethyl)-2′-deoxyuridine (14); under more vigorous conditions 5-(1-butoxyethyl)uracil (13) was formed. In 1 M hydrochloric acid at 100 °C compound (1) reacts with phenol to give a mixture of substituted phenols. From this mixture 2′-deoxy-5-[1-(4-hydroxyphenyl)ethyl]uridine (17) was isolated and characterised. In a similar manner compound (1) reacted with 4-propan-2-ylphenol to give 2′-deoxy-5-[1-(2-hydroxy-5-propan-2-ylphenyl)ethyl]uridine (18). Treatment of compound (1) with m-chloroperbenzoic acid in water–tetrahydrofuran gave 2′-deoxy-5-(1,2-dihydroxyethyl)uridine (19) which was characterised as its tetra-O-acetate (20).

Solution structures of some ‘uridine dialdehyde’ derivatives

When uridine is oxidised with periodate, the product is ‘uridine dialdehyde.’ Contrary to a previous report we have shown by 1H n.m.r. spectroscopy that in solution, this compound is not polymeric but consists of a large number of isomers in dynamic equilibrium, although even at 400 MHz the spectrum is too complicated to analyse fully. However if the 5′-OH group is not present, such as in 5′-azido-5′-deoxyuridine dialdehyde or 5′-O-trityluridine dialdehyde, only three diastereoisomeric cyclic acetals are present. The 1H n.m.r. spectrum at 400 MHz of the latter compound has been completely analysed and the identity and amounts of each of the three diastereoisomers have been determined.

Synthetic analogues of polynucleotides. Part 15. The synthesis and properties of poly(5′-amino-3′-O-carboxymethyl-2′,5′-dideoxy-erythro-pentonucleosides) containing 3′(O)→ 5′(C) acetamidate linkages

Poly(5′-amino-3′-O-carboxymethyl-5′-deoxythymidine) was prepared by the polymerisation of 5′-chloroacetamido- 5′-deoxythymidine under basic conditions to give a polymer which contained in addition to 3′(O)→5′(C) acetamidate linkages, a substantial proportion of 3′(O)→3-acetamidate linkages. To obtain a polymer which contains 3′(O)→ 5′(C) linkages, 5′-amino-5′-deoxythymidinylacetamido[3′(O)→ 5′(C)]·5′-deoxythymidin-3′-ylacetic acid (7) was synthesised and polymerised. Compound (7) was obtained by the reduction of the corresponding 5′-azido compound. The latter was obtained by the condensation of the pentachlorophenyl ester of 5′-azido-3′-O-carboxymethyl-5′-deoxythymidine with 5′-amino-3′-O-carboxymethyl-5′-deoxythymidine. Poly (5′-amino -3′-O-carboxymethyl-2′,5′-dideoxycytidine) was obtained by the polymerisation of 4-N-acetyl-5′-chloroacetamido-2′.5′-dideoxycytidine (10) under basic conditions followed by removal of the 4-N-acetyl groups by mild acidic hydrolysis. This polymer contained 3′(O)→ 5′(C) acetamidate linkages and probably <6% of other acetamidate linkages. Compound (10) was obtained from the corresponding 5′-p-tolylsulphonyloxy compound via the 5′-azido compound. None of these polymers showed any evidence of base stacking or of interaction with their complementary polyribonucleotides.