Preparation of the pure diastereomeric forms of S-(5'-deoxy-5'-adenosyl)-1-ammonio-4-methylsulfonio-2-cyclopentene and their evaluation as irreversible inhibitors of S-adenosylmethionine decarboxylase from Escherichia coli

The conformationally restricted S-adenosylmethionine analogue AdoMac [S-(5'-deoxy-5'-adenosyl)-1-ammonio-4-methylsulfonio-2-cyclopenten e] has been shown to act as an enzyme activated, irreversible inhibitor of the Escherichia coli form of the enzyme S-adenosylmethionine decarboxylase. Inactivation of the enzyme is presumably initiated by formation of an imine linkage between the inhibitor and the terminal pyruvate of the enzyme, followed by base-catalyzed elimination of methylthioadenosine and generation of a latent electrophile. Removal of the driving force for the elimination of methylthioadenosine resulted in a reversibly binding inhibitor. Thus, the thioether analogue corresponding to AdoMac, and the corresponding dihydro derivative (H2-AdoMac), reversibly inhibit the enzyme. AdoMac was resolved into its four pure diastereomeric forms, and each diastereomer was evaluated as an irreversible inhibitor of the enzyme. The KI values for the individual diastereomers range between 3.83 and 39.6 microM, with the cis-1S,4R diastereomer being the most potent inhibitor. However, the kinact values for the four diastereomers are not significantly different, suggesting that the binding of each diastereomer to the enzyme is configuration-dependent, while the subsequent inactivation likely proceeds through a single intermediate which is formed from each of the four diastereomers. Since each pure diastereomer represents a distinct conformational mimic exhibiting restricted sidechain rotation, the data suggests that these and related analogues may be useful as conformational probes for the catalytic site of AdoMet-DC.

[The role of ultraviolet and gamma radiation in the abiogenic synthesis of nucleotides in the solid state]

A possibility of abiogenic synthesis of natural nucleotides in solid state under the influence of UV and gamma radiation has been shown for a mixture of nucleosides and dihydrophosphate. Adenosine and deoxyadenosine were used as initial substances. During adenosine and deoxyadenosine phosphorylation under the action of UV radiation (lambda = 254 nm), only 5'-monophosphates were formed, a yield of 0.094 and 0.36% respectively. Under the action of gamma radiation, 2',3'-cAMP (0.12%), 2'-AMP (0.08%) and 3'-AMP (0.14%) were produced together with 5'AMP (0.41%).

Adenosine-5'-carboxaldehyde: a potent inhibitor of S-adenosyl-L-homocysteine hydrolase

Adenosine-5'-carboxaldehyde (3) and its 4'-epimer (4) were synthesized and shown to be potent type I mechanism-based inhibitors of recombinant rat liver AdoHcy hydrolase with k2/KI values of 16.7 x 10(-3) and 5.5 x 10(-3) nM-1 min-1, respectively. The observation that 3 and 4 are potent inhibitors of AdoHcy hydrolase supports the hypothesis that they function as key intermediates in the mechanism by which the (Z)- and (E)-4',5'-didehydro-5'-deoxy-5'-fluoroadenosines 1 and 2 inactivate this enzyme.

Synthesis and biological activity of 2-substituted analogues of 2'-deoxy-2'-fluoroadenosine

Reaction of 2-iodo-6-methoxypurine 2'-deoxy-2'-fluororiboside with ammonia in methanol gave 2-iodo-adenosine derivative 2 in 69% yield. Treatment of 2 with nucleophiles gave 2-substituted analogues of 2'-deoxy-2'-fluoroadenosine. A new 2'-deoxy-2,2'-difluoroadenosine was also prepared by way of quaternary salt 4.

Synthesis of 2'-deoxy-7,8-dihydro-8-oxoguanosine and 2'-deoxy-7,8-dihydro-8-oxoadenosine and their incorporation into oligomeric DNA

Reliable methods have been developed for the synthesis of the 3'-O-[(diisopropylamino) (2-cyanoethoxy)phosphino]-5'-O-(4,4'- dimethoxytrityl) derivatives of 2'-deoxy-7,8-dihydro-8-oxoguanosine (8-oxo-dGuo, 1) and 2'-deoxy-7,8-dihydro-8-oxoadenosine (8-oxo-dAdo, 2), and for the efficient incorporation of the latter into oligomeric DNA. Both methods rely on the conversion of the 2'-deoxy-8-bromopurine nucleosides 3 and 10 to their corresponding 2'-deoxy-8-(benzyloxy) nucleosides 4 and 12 followed by catalytic hydrogenation to generate the 8-oxo function at the C-8 position. The preparation of the phosphoramidites 8 and 19 required for the synthesis of a series of DNA oligomers was carried out under strictly anhydrous conditions. Failure to keep the systems dry resulted in great difficulties during the purification procedures, and erratic results when DNA synthesis was attempted. In the preparation of the DNA itself, it was found to be extremely important during the ammonia deprotection step to add an antioxidant. Otherwise aerial oxidation resulted in almost complete loss of the oligomer. However, when these special conditions were followed, oligomeric DNA containing 8-oxo-dGuo and 8-oxo-dAdo residues could be prepared in excellent yield. Analysis of selected DNA oligomers by enzymatic degradation and mass spectroscopic analysis confirmed the designated sequences and compositions.

S-(5'-deoxy-5'-adenosyl)-1-ammonio-4-(methylsulfonio)-2-cyclopentene: A potent, enzyme-activated irreversible inhibitor of S-adenosylmethionine decarboxylase

The compound S-(5'-deoxy-5'-adenosyl)-1-ammonio-4-(methylsulfonio)-2- cyclopentene (AdoMac) was prepared and evaluated as an irreversible inhibitor of S-adenosylmethionine decarboxylase (AdoMet-DC). AdoMac was shown to inhibit AdoMet-DC in a time-dependent manner with a KI of 18.3 microM and a kinact of 0.133 min-1. In addition, AdoMet-DC activity could not be restored following extensive dialysis of the enzyme-inhibitor complex, and the enzyme was protected from irreversible inactivation by the known competitive inhibitor methylglyoxal bis(guanylhydrazone). HPLC analysis of the enzymatic reaction products revealed a time-dependent decrease in the peak coeluting with AdoMac, and a corresponding increase in the peak coeluting with (methylthio)adenosine (MTA), a byproduct of the irreversible binding of AdoMac to the enzyme. Thus, AdoMac appears to function as an enzyme-activated, irreversible inhibitor of AdoMet-DC.

Nucleic acid related compounds. 74. Synthesis and biological activity of 2'(and 3')-deoxy-2'(and 3')-methylenenucleoside analogues that function as mechanism-based inhibitors of S-adenosyl-L-homocysteine hydrolase and/or ribonucleotide reductase

Treatment of 2-amino-6-chloro-9-(beta-D-ribofuranosyl)purine (21) with TBDMS chloride/imidazole/DMF gave a separable mixture of 5'-O, 2',5'-bis-O (22), 3',5'-bis-O (23), and 2',3',5'-tris-O-TBDMS derivatives. Oxidation of 22 and 23 with CrO3/pyridine/Ac2O, treatment of the respective ketonucleosides with methylenetriphenylphosphorane, and deprotection gave 2-amino-6-chloro-9-[3(and 2)-deoxy-3(and 2)-methylene- beta-D-erythro-pentofuranosyl]purines (28 and 37) that were converted into other 2-amino-6-substituted-purine analogues. Tubercidin was converted into 2'-deoxy-2'-methylenetubercidin (49) by an analogous route. Inactivation of S-adenosyl-L-homocysteine hydrolase by 2'- and 3'-methyleneadenosine analogues was investigated. Mechanism-based inhibition of S-adenosyl-L-homocysteine hydrolase and anticancer and antiviral activities of 2'(and 3')-deoxy-2'(and 3')-methylenenucleoside analogues are discussed.

A new and potent 2-5A analogue which does not require a 5'-polyphosphate to activate mouse L-cell RNase L

In order to explore the possibility of supplanting the requirement of a 5'-triphosphate moiety for the activation of the 2-5A-dependent endonuclease (RNase L) of mouse L-cells, two new tetrameric analogues of 2-5A were synthesized. The first tetramer, obtained by both a modified prebiotic synthetic approach as well as a phosphite triester solid phase oligonucleotide synthesis method, was p5'A2'p5'A2'p5'(br8A)2'p5'(br8A). The second oligonucleotide was derived from the former by a sequence involving periodate oxidation, reaction with n-hexylamine, and cyanoborohydride reduction, resulting in conversion of the 2'-terminal adenosine residue to 9-(3'-aza-4'-hexyl-1',2',3',4'-tetradeoxyhexopyranos-1(1)-yl)-8-++ +bromoadenine. Both of these oligomers, bearing only 5'-monophosphate groups, were found to be as potent as 2-5A itself as activators of the RNase L of mouse L-cells.

Incorporation of a complete set of deoxyadenosine and thymidine analogues suitable for the study of protein nucleic acid interactions into oligodeoxynucleotides. Application to the EcoRV restriction endonuclease and modification methylase

A complete set of dA and T analogues designed for the study of protein DNA interactions has been prepared. These modified bases have been designed by considering the groups on the dA and T bases that are accessible to proteins when these bases are incorporated into double-helical B-DNA [Seeman, N. C., Rosenberg, J. M., & Rich, A. (1976) Proc. Natl. Acad. Sci. U.S.A. 73, 804-808]. Each of the positions on the two bases, having the potential to interact with proteins, have been subject to nondisruptive, conservative change. Typically a particular group (e.g., the 6-NH2 of dA or the 5-CH3 of T) has been replaced with a hydrogen atom. Occasionally keto groups (the 2- and 4-keto oxygen atoms of T) have been replaced with sulfur. The base set has been incorporated into the self-complementary dodecamer d(GACGATATCGTC) at the central d(ATAT) sequence. Melting temperature determination shows that the modified bases do not destabilize the double helix. Additionally, circular dichroism spectroscopy shows that almost all the altered bases have very little effect on overall oligodeoxynucleotide conformation and that most of the modified oligomers have a B-DNA type structure. d(GATATC) is the recognition sequence for the EcoRV restriction modification system. Initial rate measurements (at a single oligodeoxynucleotide concentration of 20 microM) have been carried out with both the EcoRV restriction endonuclease and modification methylase. This has enabled a preliminary identification of the groups of the dA and T bases within the d(GATATC) sequence that make important contacts to both proteins.

Synthesis and cytotoxicity of deoxyadenosine analogues: isomer distribution in the sodium salt glycosylation of 2,6-disubstituted purines

Several 2-substituted deoxyadenosine derivatives were synthesized and screened for cytotoxicity toward hematopoietic cells in culture. To prepare intermediates for these syntheses, the sodium salts of 2,6-dibromopurine and 2,6-bis(methylthio)purine were reacted with 1-chloro-3,5-di-p-toluyl-alpha-D-erythro-pentofuranose in acetonitrile. Similar reactions using 6-chloropurines have been reported to give only 9-beta and 7-beta nucleosides as major and minor products, respectively. 2,6-Dibromopurine, however, gave 9-beta and 9-alpha isomers as major and minor products, along with a lesser amount of the 7-beta isomer. 2,6-Bis(methylthio)purine, in contrast, produced 9-beta and 7-beta isomers as major and minor products. These results are discussed in terms of sugar anomerization and possible steric and kinetic effects of base substituents in the sodium salt glycosylation reaction. Reactions of the 9-beta nucleoside isomers with ammonia and alkylamines produced several 2-bromo, 2-methylthio, and 2-amino deoxyadenosines. All of the compounds showed weaker cytotoxic activity than 2-bromodeoxyadenosine against hematopoietic cells in culture, when [14C]leucine incorporation into cellular proteins was measured.

Synthesis of the 2-chloro analogues of 3'-deoxyadenosine, 2',3'-dideoxyadenosine, and 2',3'-didehydro-2',3'-dideoxyadenosine as potential antiviral agents

2-Chloro-3'-deoxyadenosine (2-chlorocordycepin), 2-chloro-2',3'-dideoxyadenosine (2-ClddAdo), and 2-chloro-2',3'-didehydro-2',3'-dideoxyadenosine (2-ClddeAdo) were synthesized from 2-chloroadenosine (2-ClAdo) as candidate antiretroviral agents on the basis that 2-chloro substitution would prevent enzymatic deamination and increase efficacy relative to 2',3'-dideoxyadenosine (ddAdo). Reduction of 2-chloro-5'-(4,4'-dimethoxytrityl)-2',3'-O-thiocarbonyladenosine with n-Bu3SnH, followed by detritylation with AcOH, unexpectedly gave a mixture of 2-chlorocordycepin and 2-chloroadenine. Treatment of the crude n-Bu3SnH reduction product with 1,1'-thiocarbonyldiimidazole, followed by another cycle of n-Bu3SnH reduction and detritylation with silica gel afforded 2-ClddAdo and a byproduct identified as 2-chloro-2',3'-O-methyleneadenosine. Treatment of 2-chloro-5'-O-(4,4'-dimethoxytrityl)-2',3'-thiocarbonyladenosine with 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine followed by silica gel detritylation afforded 2-ClddeAdo. 2-ClddAdo and 2-ClddeAdo were tested for activity against human immunodeficiency virus (HIV) in a cultured human T4+ lymphocyte cell line. At a concentration of 100 microM, 2-ClddAdo inhibited reverse transcriptase (RT) production by 97%, while 2',3'-dideoxyadenosine (ddAdo) gave greater than 99% inhibition. In growth assays against uninfected T4+ cells, however, 100 microM 2-ClddAdo gave 23% inhibition while 100 microM ddAdo was nontoxic. At a nontoxic concentration of 20 microM, RT production was 75% inhibited by ddAdo but only 43% inhibited by 2-ClddAdo. Thus, a 2-chloro substituent increased host cell toxicity but decreased antiretroviral activity. The unsaturated analogue 2-ClddeAdo was more cytotoxic than 2-ClddAdo, and antiviral effects could not be measured above 20 microM, where there was only 75% inhibition of RT production. Because of the decreased therapeutic index of 2-ClddeAdo relative to 2-ClddAdo and ddAdo, greater than 90% inhibition of viral protein synthesis at a noncytotoxic concentration could not be achieved. In growth assays with cultured human T and B lymphocytes, 100 microM 2-chlorocordycepin gave 60-70% growth inhibition, while the IC50 against mouse fibroblasts was only 30 microM. The high cytotoxicity of 2-chlorocordycepin precluded consideration of this compound as an antiviral agent.

Synthesis and anti-HIV activity of various 2'- and 3'-substituted 2',3'-dideoxyadenosines: a structure-activity analysis

A systematic synthesis was undertaken of 2',3'-dideoxyadenosine analogues with either an azido, fluorine, or hydroxyl group substituted in the "up" or "down" position of C-2 or C-3 of the sugar moiety. The compounds were evaluated against the cytopathogenicity of human immunodeficiency virus (HIV) for MT-4 cells. The four azido derivatives 6, 7, 8, and 9 were synthesized by a nucleophilic displacement reaction with lithium azide on the mesylates 3, 2, 5, and 4. (Diethylamido)sulfur trifluoride was used for the synthesis of 10-12. The compound 13 was obtained by 2'-deoxygenation of 9-(3-fluoro-3-deoxy-beta-D-xylofuranosyl)adenine. Among the azido derivatives, compound 8 with the 3'-azido "down" was slightly more active than 2',3'-dideoxyadenosine (1) but considerably more toxic, and, of the fluorine series, compound 11, with the 2'-fluoro "up", was the most selective inhibitor of HIV, although it was less active than 1. Hence, none of the newly synthesized compounds proved more selective in their anti-HIV activity than the parent compound, 1.

15N labeling of oligodeoxynucleotides for NMR studies of DNA-ligand interactions

The amino protons of 15N-labeled DNA were studied as a possible structural probe in NMR investigations of the interaction of DNA with various ligands. Since the imino protons are located in the center of the double helix, and variations of their chemical shift values are difficult to interpret in terms of structural changes, these probes are not very useful. Instead, amino protons are located in the major or minor groove of the DNA and are often directly involved in the binding of a ligand. For a selective probing 4-15NH2-2'-deoxycytidine and 6-15NH2-2'-deoxyadenosine were obtained by chemical synthesis. The labeled nucleosides were introduced in distinct positions of oligodeoxynucleotides by large-scale DNA synthesis. Direct 15N NMR and 1H-15N multiple quantum NMR were applied to detect the corresponding 15N labels or protons attached to the 15N labels. Chemical shift values for the cytidine and the adenosine amino nitrogen and proton resonances of a symmetric 18 base pair lac operator sequence are reported.

Inhibition of muscarinic receptor binding and acetylcholine-induced contraction of guinea pig ileum by analogues of 5'-(isobutylthio)adenosine

(Isobutylthio)adenosine (SIBA, 1) and its derivatives have been shown to produce a variety of biological effects on the basis of the hypothesis that such agents act directly as inhibitors of transmethylation reactions, as inhibitors of S-adenosylhomocysteine hydrolase, or as inhibitors of polyamine biosynthesis. We report here the ability of selected analogues of SIBA to inhibit the binding of the muscarinic antagonist quinuclidinyl benzilate (QNB) to cultured N4TG1 neuroblastoma cells and to antagonize the acetylcholine-induced contraction of guinea pig ileum. The most potent inhibitors were 5'-deoxy-5'-(isobutylthio)-1-deazaadenosine (1-deaza-SIBA, 5) and 5'-deoxy-5'-(isobutylthio)-3-deazaadenosine (3-deaza SIBA, 3), while the parent nucleoside SIBA and the carbocyclic derivative 5'-(isobutylthio)-3-deazaaristeromycin were less active. The same agents had no effect on the nicotinic receptors of NG108-15 neuroblastoma X glioma hybrid cells. The acyclic derivative 9-[[2-(isobutylthio)ethoxy]methyl]adenine, 3-deazaadenosine, 5'-(isobutylthio)tubercidin, and 5'-(isobutylamino)adenosine were inactive at the 1-mM level. These results suggest that SIBA and 3-deaza-SIBA may have profound effect on membrane-mediated phenomenon, including inhibition of muscarinic receptor binding.

Improved synthesis and antitumor activity of 2-bromo-2'-deoxyadenosine

A more convenient synthetic route to 2-bromo-2'-deoxyadenosine (5) is reported, and results indicating significant antitumor activity of 5 against three murine tumors (L1210 leukemia, B16 melanoma, and M5076 ovarian carcinoma) are presented. The antitumor activity is very schedule dependent, being much greater when the drug is given q 3 h (X8) every 3rd or 4th day than when given by single daily administration. Toxicity of 5 for the tumor-bearing host is also very schedule dependent. Thus, on the q 3 h schedule of administration, a greater cumulative dose is tolerated by the host, and the therapeutic effectiveness of 5 is enhanced accordingly.

5'-bromoacetamido-5'-deoxyadenosine. A novel reagent for labeling adenine nucleotide sites in proteins

We have synthesized and characterized 5'-bromoacetamido-5'-deoxyadenosine (5'-BADA), a new reagent for labeling adenine nucleotide binding sites in enzymatic and regulatory proteins. 5'-BADA possessed exceptionally high solubility and stability in aqueous buffers between pH 5.0 and 8.6 at 25 degrees C. A Dixon plot of data from enzyme kinetic measurements showed that 5'-BADA is a competitive inhibitor of NADH oxidation by 3 alpha,20 beta-hydroxysteroid dehydrogenase with a Ki value of 11.8 mM. This compares with a Ki value of 10 mM for adenosine under similar experimental conditions. Incubating 5'-BADA with a 3 alpha,20 beta-hydroxysteroid dehydrogenase at pH 7.0 and 25 degrees C caused simultaneous loss of both 3 alpha and 20 beta activity. The enzyme inactivation reaction proceeded by a first order kinetic process. The rates of enzyme inactivation as a function of 5'-BADA concentration obeyed saturation kinetics. 2-Bromoacetamide, at ten times the maximum concentration of 5'-BADA, had no measurable effect on enzyme activity during 25 h of incubation. NADH and AMP protected 3 alpha,20 beta-hydroxysteroid dehydrogenase against inactivation by 5'-BADA. The results suggest that 5'-BADA inactivates the enzyme by irreversibly binding to the adenine domain of the NADH cofactor binding region at the catalytic site of 3 alpha,20 beta-hydroxysteroid dehydrogenase. Irreversible binding follows from an alkylation reaction between the bromoacetamido side chain of 5'-BADA and an amino acid at or near the enzyme catalytic site. 5'-BADA is presented as a new reagent for selectively labeling amino acid residues at the adenine nucleotide binding sites of enzymatic and regulatory proteins.

[An effective inhibitor of S-adenosylmethionine decarboxylase]

New analogues of cAMP, namely 2'-phosphate of cAMP and its esters, were obtained by direct phosphorylation of N6-benzoyladenosine 3',5'-cyclic phosphate with 2-cyanoethyl phosphate in the presence of DCC followed by the removal of protecting groups.

Preparation of the alpha and beta anomers of 9-(3,5-dideoxy-D-glycero-pent-4-enofuranosyl)adenine and their activity with leukemia L1210 cells in vitro

A previously reported preparation of 9-(3,5-dideoxy-beta-D-glycero-pent-4-enofuranosyl)adenine (5) was not correct. A new synthesis of 5 is described. 3,5-Dideoxy-5-iodo-1,2-O-isopropylidene-alpha-D-erythro-pentofuranose (1) and 3,5-dideoxy-5-iodo-1,2-O-isopropylidene-beta-L-threo-pentofuranose (6) were prepared as starting materials. The isopropylidene groups were exchanged for acetyl groups by acetolysis, and the resulting diacetates (2 and 7) were isopropylidene groups were coupled with 6-(benzamidochloromercuri)purine by the titanium tetrachloride method. The blocked nucleosides (3 and 8) were separated from unreacted sugars by chromatography and were treated with 1,8-diazabicyclo-[5.4.0]undec-7-ene, followed by removal of the blocking groups. The alpha and beta anomers of 9-(3,5-dideoxy-D-glycero-pent-4-enofuranosyl)adenine (4 and 5, respectively) were obtained from 3 in the ratio of 3:1. Condensation of 7 with the base gave the beta-nucleoside 5 in a higher yield; no 4 was detected. When 8 was treated with sodium benzoate in hot DMF and the blocking groups were removed, 9-(5-methyl-2-furyl)adenine (9) and 9-(3-deoxy-alpha-benzoate in hot DMF and the blocking groups were removed, 9-(5-methyl-2-furyl)adenine (9) and 9-(3-deoxy-alpha-L-threo-pentofuranosyl)adenine (10) were the products. It was demonstrated that sodium benzoate was solely responsible for formation of the 5-methyl-2-furyl ring and that the first step was formation of the 4',5'-olefin.

Binding specificities of adenosine aminohydrolase from calf intestinal mucosa with dialdehydes derived from hexofuranosyladenine nucleosides

A series of nucleoside dialdehydes has been prepared as powders after treatment of hexofuranosyladenine nucleosides with paraperiodic acid; thus, periodate oxidation and purification of the products yielded dialdehydes derived from 9-(6-deoxy-beta-D-gulofuranosyl)adenine (1), 9-(6-deoxy-beta-L-gulofuranosyl)adenine (2), 9-(alpha-D-rhamnofuranosyl)adenine (3), 9-(alpha-L-rhamnofuranosyl)adenine (4), 9-(6-deoxy-alpha-L-talofuranosyl)adenine (5), 9-(5,6-dideoxy-beta-L-ribo-hex-5-enofuranosyl)adenine (6), and 9-(5,6-dideoxy-beta-D-ribo-hex-5-enofuranosyl)adenine (7). Nucleoside dialdehydes 1, 4, and 5 were weak substrates for adenosine aminohydrolase from calf intestinal mucosa. Dialdehydes 6 and 7 were not substrates for the enzyme but were rather strong competitive inhibitors, with Ki values of 50 and 7 microM, respectively. Dialdehydes 2 and 3 did not bind to the enzyme at all. The dialdehydes did not exhibit time-dependent inhibition, suggesting that they did not form covalent bonds with the protein.

Preparation of the enantiomeric forms of 9-(5-deoxy-alpha-threo-pent-4-enofuranosyl)adenine and 9-(3,5-dideoxy-beta-D-glycero-pent-4-enofuranosyl)adenine and in vitro antileukemic screening

The preparation and use of 5-deoxy-5-iodo-1,2-O-isopropylidene-alpha-D-xylofuranose and 5-deoxy-5-iodo-1,2-O-isopropylidene-alpha-D-arabinofuranose in the synthesis of the L and D forms of 9-(5-deoxy-alpha-threo-pent-4-enofuranosyl)adenine, respectively, are described. The preparation of 9-(3,5-dideoxy-beta-D-glycero-pent-4-enofuranosyl)adenine (19) was accomplished from either 3,5-dideoxy-5-iodo-1,2-O-isopropylidene-alpha-D-erythro-pentofuranose or 3,5-dideoxy-5-iodo-1,2-O-isopropylidene-beta-L-threo-pentofuranose. In each case, acetolysis was performed to obtain the acetates which were condensed with 6-(benzamidochloromercuri)purine by the titanium tetrachloride method. Treatment with 1,5-diazabicyclo[5.4.0]undec-5-ene and removal of the blocking groups produced the desired nucleosides. Only 19 showed inhibitory activity toward leukemia L1210 in vitro.

Synthesis and thermal melting behavior of oligomer-polymer complexes containing defined lengths of mismatched dA-dG and dG-dG nucleotides

Model DNA polymers containing heteroduplex regions of defined sequence and size were synthesized using polynucleotide phosphorylase and calf thymus terminal transferase. Heteroduplexes were of the form (dG)n-d(C12AmC-x), where m - 1-6, and (dG)n-d(C10GmC-x), where m = 1 and 3-5. Thermal melting studies of the model DNAs indicated that the heteroduplex regions did not disrupt the cooperative interaction between the flanking regions of dG-dC base pairs. thus, it is possible that the heteroduplex nucleotides are accommodated in a stacked helical structure.

Enantiomeric forms of 9-(5-deoxy-beta-erythro-pent-4-enofuranosyl)adenine and a new preparation of 5-deoxy-D-lyxose

Methyl 5-deoxy-5-iodo-2,3-O-isopropylidene-beta-D-ribofuranoside (3) was obtained in three steps from D-ribose. Exchange of the isopropylidene group for benzoate groups and acetolysis gave 1-O-acetyl-2,3-di-O-benzoyl-5-deoxy-5-iodo-D-ribofuranose which was coupled with 6-benzamidochloromercuripurine by the titanium tetrachloride method to afford the blocked nucleoside. Treatment with 1,5-diazabicyclo[5.4.0]undec-5-ene in N,N-dimethylformamide and removal of the blocking groups have 9-(5-deoxy-beta-D-erythro-pent-4-enofuranosyl)adenine (9). A similar route starting from methyl 5-deoxy-5-iodo-2,3-O-isopropylidene-alpha-D-lyxofuranoside (14) afforded the enantiomeric nucleoside, 9-(5-deoxy-beta-L-erythro-pent-4-enofuranosyl)adenine (20). Methyl 2,3-O-isopropylidene-alpha-D-mannofuranoside was treated with sodium periodate and then with sodium borohydride to give methyl 2,3-O-isopropylidene-alpha-D-lyxofuranoside (11). Acid hydrolysis afforded D-lyxose. Tosylation of 11 gave methyl 2,3-O-isopropylidene-5-O-p-tolylsulfonyl-alpha dp-lyxofuranoside (12) which was converted into 14 with sodium iodide in acetone. Reduction of 12 gave methyl 5-deoxy-2,3-O-isopropylidene-alpha-D-lyxofuranoside which was hydrolyzed to give 5-deoxy-D-lyxose.

Nucleosides. 1. 9-(3'-Alkyl-3'-deoxy-beta-D-ribofuranosyl)adenines as lipophilic analogues of cordycepin. Synthesis and preliminary biological studies

A series of lipophilic 9-(3'-alkyl-3'-deoxy-beta-D-ribofuranosyl)adenines of increasing chain length was synthesized from the corresponding branched sugars via titanium chloride catalyzed ribosylation of chloromercuri-6-benzamidopurine. Enhanced growth inhibitory activity was observed against (CCRF-CEM human lymphoblastic leukemia cells in culture as the length of the alkyl side chain in the sugar and the resultant lipophilic character of the nucleoside were increased. Experiments involving incorporation of radiolabeled uridine, thymidine, and leucine revealed that in contrast to cordycepin (1) the 3'-n-butyl and 3'-n-hexyl analogues 5 and 6 markedly inhibit not only RNA synthesis but DNA and protein synthesis as well.