Nucleosides and nucleotides. 177. 9-(6,7-dideoxy-beta-D-allo-hept-5- ynofuranosyl)adenine: a selective and potent ligand for P3 purinoceptor-like protein

Effect of uridine protecting groups on the diastereoselectivity of uridine-derived aldehyde 5'-alkynylation

The 5'-alkynylation of uridine-derived aldehydes is described. The addition of alkynyl Grignard reagents on the carbonyl group is significantly influenced by the 2',3'-di-O-protecting groups (R1): O-alkyl groups led to modest diastereoselectivities (65:35) in favor of the 5'R-isomer, whereas O-silyl groups promoted higher diastereoselectivities (up to 99:1) in favor of the 5'S-isomer. A study related to this protecting group effect on the diastereoselectivity is reported.

The first radical method for the introduction of an ethynyl group using a silicon tether and its application to the synthesis of 2'-deoxy-2'-C-ethynylnucleosides

A novel radical method for the stereoselective introduction of an ethynyl group has been developed. When a solution of ethynyldimethylsilyl (EDMS) or [2-(trimethylsilyl)ethynyl]dimethylsilyl (TEDMS) ethers of trans-2-iodoindanol was treated with Et(3)B followed by tetrabutylammonium fluoride in toluene, atom transfer 5-exo-cyclization and subsequent elimination occurred to give cis-2-ethynylindanol in high yield. The method was shown to be useful in the introduction of an ethynyl group in various five- and six-membered-ring iodohydrins. Furthermore, 2'-deoxy-2'-C-ethynyluridine (6) and -cytidine (7), which were designed as novel antimetabolites, were readily synthesized by using this method as the key step. This would be the first example in which a radical reaction was used for introducing an ethynyl group.

Pharmacology of a unique adenosine binding site in rat brain using a selective ligand

1. In order to further characterize the adenosine binding sites that we previously purified and termed P3 purinergic receptor-like protein (P3LP), a reliable binding assay method was developed using [3H]-5'-N-ethylcarboxamidoadenosine (NECA) as a radioligand and the newly developed high-affinity selective ligand 9-(6,7-dideoxy-beta-D-allo-hept-5-ynofuranosyl) adenine (HAK2701) as a selective displacer. 2. Using this assay method, it was found that rat brain membranes possess high- and low-affinity [3H]-NECA binding sites. The high-affinity binding site showed KD and Bmax values of 19.7+/-2.5 nmol/L and 0.192+/-0.05 pmol/mg protein, respectively, and the KD value for the low-affinity binding site was 4260+/-330 nmol/L. The KD value for the high-affinity site agreed well with that of the [3H]-NECA binding site determined with the partially purified P3LP preparation described previously. 3. The distribution of P3LP in rat tissues was determined using the [3H]-NECA binding method described above. The highest level of P3LP was in the cerebellum followed by the olfactory bulb and the spinal cord. 4. The order of the affinity for various purinergic or related compounds to P3LP in rat brain preparations was also determined by the [3H]-NECA binding method to be HAK2701 > NECA = adenosine 5'-O-(2-thiodiphosphate) > cAMP = beta,gamma-methyleneadenosine 5'-triphosphate > diadenosine tetraphosphate > alpha,beta-methyleneadenosine 5'-triphosphate > 5'-deoxy-5'-methylthioadenosine > N6-cyclopentyladenosine. 5. These studies reveal that the [3H]-NECA binding assay in combination with HAK2701 is successful in the characterization of P3LP, especially the membrane-bound form.

Effect of 9-(6,7-dideoxy-beta-D-allo-hept-5-ynofuranosyl)adenine on noradrenaline release from vascular sympathetic nerves

1. The effects of 9-(6,7-dideoxy-beta-D-allo-hept-5-ynofuranosyl)adenine (HAK2701), a selective and potent ligand for P3 receptor-like protein, on the release of endogenous noradrenaline (NA) from electrically stimulated rat mesenteric artery and rabbit ear artery were compared with those of a number of purinoceptor agonists. 2. In the rat mesenteric artery, the P1 receptor agonists 2-chloroadenosine (2CA) and 5'-N-ethylcarboxamidoadenosine (NECA) and the P2 purinoceptor agonists beta,gamma-methylene ATP (betagammamATP) and 2-methylthio ATP (2mSATP) significantly inhibited the release of NA in a xanthine-sensitive manner. HAK2701 did not significantly inhibit the release of NA, the relative order of potency being betagammamATP > NECA > 2CA > 2mSATP >> HAK2701. 3. In the rabbit ear artery, both P1 and P2 receptor agonists significantly facilitated the release of NA in a xanthine-sensitive manner. HAK2701 also significantly facilitated the release of NA, the relative order of potency being HAK2701 > betagammamATP > 2CA > 2mSATP > NECA. 4. These findings suggest that HAK2701 may be a potent and selective agonist for facilitatory prejunctional purinoceptors, but not for inhibitory purinoceptors, on adrenergic nerve terminals.

Nucleosides and nucleotides. 200. Reinvestigation of 5'-N-ethylcarboxamidoadenosine derivatives: structure-activity relationships for P(3) purinoceptor-like proteins

The non-P(1) and non-P(2) muscle relaxant effect of ATP in rabbit thoracic aorta has recently been attributed to a putative P(3) purinoceptor, which is activated by either adenosine or ATP. Since the physiological roles of this putative P(3) purinoceptor and of a new [(3)H]-5'-N-ethylcarboxamidoadenosine (NECA)-binding protein from rat brain membranes called P(3) purinoceptor-like protein (P(3)LP), due to its ligand specificity, have not been fully elucidated, we needed a specific ligand to obtain further information about the receptor. We examined the structure-activity relationship (SAR) of various 5'-N-substituted-carboxamidoadenosine derivatives toward P(3)LP and discovered a hydrophobic binding region near the 5'-N-substituted-carboxamide group. From the linear alkyl N-substituted derivatives, the N-n-pentyl derivative 10 was found to be the most potent ligand with a K(i) value of 12 nM. In the series of the N-cycloalkyl derivatives, the N-cyclohexyl derivative 27 was the strongest ligand with a K(i) value of 18 nM. On the other hand, the N-substituents having branched alkyl side chains and bulky cycloalkyl groups did not show any potent affinities for P(3)LP. Therefore, the hydrophobic pocket accommodates approximately a 10-carbon-atom-long linear alkyl side chain, while a considerably stronger hydrophobic binding region of about a 5-carbon-atom-long depth exists near the nitrogen atom of the amide group. This pocket also allows substitution with bulky hydrophobic groups since the 5'-N-cycloalkyl derivatives have high affinities. We also examined the receptor selectivity for the selected nucleosides 10 and 27 with 1 [9-(6,7-dideoxy-beta-D-allo-hept-5-ynofuranosyl)adenine, HAK2701] and NECA versus P(1) purinoceptor subtypes, such as adenosine A(1), A(2A), A(2B), and A(3) receptors, and found that 27 is the most selective ligand for P(3)LP.