Life-history traits of the long-nosed skate Dipturus oxyrinchus.

This work investigates life-history traits of the long-nosed skate Dipturus oxyrinchus, which is a common by-catch in Sardinian waters. The reproductive variables were analysed from 979 specimens sampled during scientific and commercial hauls. Females (10·4-117·5 cm total length, LT ) attained larger sizes than males (14·5-99·5 cm LT ). To evaluate age and growth, a sub-sample of 130 individuals (76 females and 54 males) were used. The age was estimated by annuli counts of sectioned vertebral centra. Four models were used for the length-at-age data: the von Bertalanffy, the exponential, the Gompertz and the logistic functions. According to the Akaike's information criterion, the Gompertz model seemed to provide the best fitting curve (L∞ mean ± s.e.: 127·55 ± 4·90 cm, k: 0·14 ± 0·09, IP: 3·97 ± 0·90 years). The oldest female and male were aged 17 (115·5 cm LT ) and 15 years (96·0 cm LT ), respectively. Lengths at maturity were 103·5 cm for females and 91·0 cm for males, corresponding to 90% of the maximum observed length in both sexes. The monthly distribution of maturity stages highlighted an extended reproductive cycle, with spawning females and active males being present almost throughout the year, as confirmed by the gonado-somatic index. Ovarian fecundity reached a maximum of 26 yolked follicles with a mean ± s.e. size of 19·7 ± 6·5 mm.

Phytochemical and antioxidant analysis of eight Hypericum taxa from Central Italy.

Eight taxa of the Hypericum spp. growing in Central Italy (Appennino Umbro-Marchigiano) were analyzed by HPLC-DAD for constituents quantitation, for antioxidant and free radical scavenging activities. H. perforatum subsp. veronense was the richest in phenolic compounds and hyperforin was detected for the first time in H. hircinum subsp. majus. Significant values of antioxidant activity were found in the investigated Hypericum taxa.

Antiviral properties of deazaadenine nucleoside derivatives.

Viral infections have menaced human beings since time immemorial, and even today new viral strains that cause lethal diseases are being discovered with alarming frequency. One major example is HIV, the etiological agent of AIDS, which spread up in the last two decades. Very recently, other virus based diseases such as avian flu have spread fear around the world, and hemorrhagic fevers from central Africa serious threaten human health because of their very deadly effects. New antiviral agents are still greatly needed to counter these menaces. Many scientists are involved in this field of research, and many of the recently discovered effective antiviral compounds are nucleoside analogues. Among those derivatives, deazapurine nucleoside analogues have demonstrated potent inhibitory effect of viral replication. This review reports on recently generated data from preparing and testing deazapurine nucleoside derivatives as inhibitors in virus replication systems. Although most of the reported data have been produced in antiHIV, antiHCMV, and antiHSV biological testing, very recently other new important fields of application have been discovered, all in topical subjects of strong interest. In fact, deazapurine nucleosides have been found to be active as chemotherapeutics for some veterinary systemic viral infections, for which no antiviral drugs are licensed yet. Furthermore, they demonstrated efficacy in the inhibition of Hepatitis C virus replication. Finally, these compounds showed high potency as virucides against Ebola Virus, curing Ebola infected mice with a single dose administration.

Ring opening reactions: synthesis of AICAR analogs as potential antimetabolite agents.

In an attempt to improve the AzA selectivity of the 2-(aryl)alkylthio derivatives of adenosine, we planned the synthesis of the corresponding derivatives of the 5-N-ethylcarboxamidoadenosine (NECA). For this purpose, we designed the synthesis of 2-mercapto-NECA to be pursued by means of an opening-closure method We obtained the open AICAR analog; however, ring closure efforts failed to give the desired compound. The newly synthesized AICAR derivative could potentially be endowed with antiviral or antitumoral activity.

3,7-Dideazapurine nucleosides. Synthesis and antitumor activity of 1-deazatubercidin and 2-chloro-2'-deoxy-3,7-dideazaadenosine.

1-Deazatubercidin (5) has been synthesized by glycosylation of the anion of 4,6-dichloro-1H-pyrrolo[3,2-c]pyridine (9) with 1-chloro-2,3-O-isopropylidene-5-O-(tert-butyldimethylsilyl)-alpha-D-r ibofuranos e (12). The reaction gave a mixture of blocked nucleosides with beta- and alpha-configuration (13a and 13b). Deprotection of 13a provided 4,6-dichloro-1-beta-D-ribofuranosylpyrrolo[3,2-c]pyridine (14), which on treatment with hydrazine, followed by reduction of the resulting 4-hydrazino compound with Raney nickel, gave 4-amino-6-chloro-1-beta-D-ribofuranosylpyrrolo[3,2-c]pyridine (15), 1-deazatubercidin, and a small quantity of 4,6-diamino-1-beta-D-ribofuranosylpyrrolo[3,2-c]pyridine (16). Dehalogenation of 15 provided another route to 5. 2-Chloro-2'-deoxy-3,7-dideazaadenosine (6) together with 2'-deoxy-3,7-dideazaadenosine (18) was obtained by hydrazinolysis of 4,6-dichloro-1-(2-deoxy-beta-D-erythro-pentofuranosyl)pyrrolo- [3,2-c]pyridine (17), followed by reduction of the resulting 4-hydrazino compound. Nucleosides 5, 6, 15, and 18 are devoid of any significant antitumor activity in vitro. Compound 16 showed significant activity against P388 leukemia in cell culture.

Adenosine deaminase inhibitors: synthesis and structure-activity relationships of imidazole analogues of erythro-9-(2-hydroxy-3-nonyl)adenine.

A series of erythro-1-(2-hydroxy-3-nonyl)imidazole derivatives have been synthesized and evaluated for adenosine deaminase (ADA) inhibitory activity, in order to introduce simplifications in the ADA inhibitors erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA, 1a) and 3-deaza-EHNA (1c). Opening the pyrimidine or pyridine ring of EHNA or 3-deaza-EHNA respectively led to compounds which are still ADA inhibitors. The most potent compound was erythro-1-(2-hydroxy-3-nonyl)imidazole-4-carboxamide (5, Ki = 3.53 x 10(-8) M), which provided potential donor and acceptor sites for hydrogen bonding. Lack of one of this sites could account for the order of potency of all compounds examined in this series. Opening the same ring in adenosine and in 3-deazaadenosine led to fully inactive compounds. These results support the hypothesis of the existence, at or near the enzyme active site, of a hydrophobic region able to bind the erythro-nonyl moiety.

Purine and 1-deazapurine ribonucleosides and deoxyribonucleosides: synthesis and biological activity.

A series of 6-(hydroxylamino)purine and -1-deazapurine nucleosides were synthesized and tested for their antitumor and adenosine deaminase inhibitory activity. All the examined molecules displayed an in vitro activity comparable to that of the reference compounds 6-(hydroxylamino)-9-beta-D-ribofuranosylpurine (HAPR) and ara-A, their ID50 ranging from 0.9 microM to approximately 100 microM. The 6-hydroxylamino derivatives of 1-deazapurine 9, 12, and 17 and also the blocked compound 13 are inhibitors of ADA whereas the purine derivatives 4 and 6 and the nitro compounds 11 and 16 are resistant to the enzyme. 7-(Hydroxylamino)-3-(2-deoxy-beta-D-erythro-pentofuranosyl)-3H-imi dazo[4,5- b]pyridine, the less cytotoxic but the most active ADA inhibitor in the series (Ki = 2.7 x 10(-7)), greatly potentiates the antitumor activity of ara-A in vitro.

Improved synthesis and antitumor activity of 1-deazaadenosine.

A more convenient synthetic route to 1-deazaadenosine (1) by reduction of the new nucleoside 7-nitro-3-beta-D-ribofuranosyl-3H-imidazo[4,5-b]pyridine (6) is reported. Compound 6 was obtained by reaction of 7-nitroimidazo-[4,5-b]pyridine with 1,2,3,5-tetra-O-acetyl-beta-D-ribofuranose in the presence of stannic chloride followed by treatment with methanolic ammonia. 1-Deazaadenosine (1) showed good activity in vitro as inhibitor of HeLa, KB, P388, and L1210 leukemia cell line growth, with ID50 values ranging from 0.34 microM (KB) to 1.8 microM (P388). The nitro derivative 6 demonstrated moderate activity against the same cell lines.

Adenosine receptor agonists: synthesis and biological evaluation of 1-deaza analogues of adenosine derivatives.

In a search for more selective A1 adenosine receptor agonists, N6-[(R)-(-)-1-methyl-2-phenethyl]-1-deazaadenosine (1-deaza-R-PIA, 3a), N6-cyclopentyl-1-deazaadenosine (1-deazaCPA, 3b), N6-cyclohexyl-1-deazaadenosine (1-deazaCHA, 3c), and the corresponding 2-chloro derivatives 2a-c were synthesized from 5,7-dichloro-3-beta-D-ribofuranosyl-3H-imidazo[4,5-b]pyridine. On the other hand, N-ethyl-1'-deoxy-1'-(1-deaza-6-amino-9H-purin-9-yl)-beta-D-ribofuranu ronamide (1-deazaNECA, 10) was prepared from 7-nitro-3-beta-D-ribofuranosyl-3H-imidazo[4,5-b]pyridine, in an attempt to find a more selective A2 agonist. The activity of all deaza analogues at adenosine receptors has been determined in adenylate cyclase and in radioligand binding studies. 1-DeazaNECA proved to be a nonselective agonist at both subtypes of the adenosine receptor. It is about 10-fold less active than NECA but clearly more active than the parent compound 1-deazaadenosine as an inhibitor of platelet aggregation and as a stimulator of cyclic AMP accumulation. The N6-substituted 1-deazaadenosines largely retain the A1 agonist activity of their parent compounds, but lose some of their A2 agonist activity. This results in A1-selective compounds, of which N6-cyclopentyl-2-chloro-1-deazaadenosine (1-deaza-2-Cl-CPA, 2b) was identified as the most selective agonist at A1 adenosine receptors so far known. The activity of all 1-deaza analogues confirms that the presence of the nitrogen atom at position 1 of the purine ring is not critical for A1 receptor mediated adenosine actions.

2-Alkynyl derivatives of adenosine and adenosine-5'-N-ethyluronamide as selective agonists at A2 adenosine receptors.

In the search for more selective A2-receptor agonists and on the basis that appropriate substitution at C2 is known to impart selectivity for A2 receptors, 2-alkynyladenosines 2a-d were resynthesized and evaluated in radioligand binding, adenylate cyclase, and platelet aggregation studies. Binding of [3H]NECA to A2 receptors of rat striatal membranes was inhibited by compounds 2a-d with Ki values ranging from 2.8 to 16.4 nM. 2-Alkynyladenosines also exhibited high-affinity binding at solubilized A2 receptors from human platelet membranes. Competition of 2-alkynyladenosines 2a-d for the antagonist radioligand [3H]DPCPX and for the agonist [3H]CCPA gave Ki values in the nanomolar range, and the compounds showed moderate A2 selectivity. In order to improve this selectivity, the corresponding 2-alkynyl derivatives of adenosine-5'-N-ethyluronamide 8a-d were synthesized and tested. As expected, the 5'-N-ethyluronamide derivatives retained the A2 affinity whereas the A1 affinity was attenuated, resulting in an up to 10-fold increase in A2 selectivity. A similar pattern was observed in adenylate cyclase assays and in platelet aggregation studies. A 30- to 45-fold selectivity for platelet A2 receptors compared to A1 receptors was found for compounds 8a-c in adenylate cyclase studies.

Synthesis and antitumor activity of 2-beta-D-ribofuranosyloxazole-4-carboxamide (oxazofurin).

Condensation of 3,4,6-tri-O-benzoyl-2,5-anhydro-D-allonyl chloride (4) with ethyl 2-amino-2-cyanoacetate (5) provided 2-[(3',4',6'-tri-O-benzoyl-2',5'-anhydroallonyl)amino]-2-cyanoa cetate (6). Compound 6 was treated with hydrogen chloride gas to give ethyl 5-amino-2-(2',3',5'-tri-O-benzoyl-beta-D- ribofuranosyl)oxazole-4-carboxylate (8). Reductive dediazotization of blocked nucleoside 8 provided ethyl 2-(2',3',5'-tri-O- benzoyl-beta-D-ribofuranosyl)oxazole-4-carboxylate (10), which after deblocking with sodium methoxide and ammonolysis was converted to 2-beta-D-ribofuranosyl-oxazole-4-carboxamide (oxazofurin, 3), an analogue of the antitumor and antiviral C-nucleoside tiazofurin (1). Oxazofurin (3) was found to be cytotoxic toward B16 murine melanoma cells in culture but inactive against murine leukemia P388 and L1210.

Adenosine deaminase inhibitors: synthesis and structure-activity relationships of 2-hydroxy-3-nonyl derivatives of azoles.

A series of erythro-1-(2-hydroxy-3-nonyl)azole derivatives have been synthesized and evaluated for adenosine deaminase (ADA) inhibitory activity, in order to introduce simplifications in the ADA inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA, 1a). The synthesis of most of the reported compounds was achieved by reaction of 2-bromo-3-nonanone with the suitable azole followed by reduction of the carbonyl group to give a diastereoisomeric mixture of N-substituted (2-hydroxy-3-nonyl)azoles. Separation of diastereoisomers was achieved by HPLC or by preparative TLC plates. The results of the enzymatic test indicate that the nitrogen in the 3-position, and secondly, the nitrogen in the 5-position are very important for the interaction of the azole ring with the inhibitory site on the enzyme. In fact, the pyrazole and the 2-substituted 1,2,3-triazole derivatives (10 and 15, respectively) are nearly inactive, whereas the erythro-1-(2- hydroxy-3-nonyl)-1,2,4-triazole (18e) was the most potent ADA inhibitor in the series with Ki = 0.3 microM.

Deoxy sugar analogues of triciribine: correlation of antiviral and antiproliferative activity with intracellular phosphorylation.

Triciribine (TCN) and triciribine monophosphate (TCN-P) have antiviral and antineoplastic activity at low micromolar or submicromolar concentrations. In an effort to improve and better understand this activity, we have conducted a structure-activity relationship study to explore requirements for the number of hydroxyl groups on the ribosyl moiety for biological activity. 2'-Deoxytriciribine (2'-dTCN), 3'-deoxytriciribine (3'-dTCN), 2', 3'-epoxytriciribine (2',3'-epoxyTCN), 2',3'-dideoxy-2', 3'-didehydrotriciribine (2',3'-d4TCN), and 2',3'-dideoxytriciribine (2',3'-ddTCN) were synthesized and evaluated for activity against human immunodeficiency virus (HIV-1), herpes simplex virus type 1 (HSV-1), and human cytomegalovirus (HCMV). Antiproliferative activity of the compounds also was tested in murine L1210 cells and three human tumor cell lines. All compounds were either less active than TCN and TCN-P or inactive at the highest concentration tested (100 microM) in both antiviral and antiproliferative assays. Reverse-phase HPLC of extracts from uninfected cells treated with the deoxytriciribine analogues only detected the conversion of 3'-dTCN and 2',3'-ddTCN to their respective monophosphates. Therefore, either the deoxytriciribine analogues were not transported across the cell membrane or, more likely, they were not substrates for a nucleoside kinase or phosphotransferase. We have concluded that the hydroxyl groups on the ribosyl ring system of TCN and TCN-P must be intact in order to obtain significant antiviral and antineoplastic activity.

2-Alkynyl derivatives of adenosine-5'-N-ethyluronamide: selective A2 adenosine receptor agonists with potent inhibitory activity on platelet aggregation.

A series of new 2-alkynyl and 2-cycloalkynyl derivatives of adenosine-5'-N-ethyluronamide (NECA) and of N-ethyl-1'-deoxy-1'-(6-amino-2-hexynyl-9H-purin-9-yl)-beta-D- ribofuranuronamide (1, HE-NECA), bearing hydroxy, amino, chloro, and cyano groups in the side chain, were synthesized. The compounds were studied in binding and functional assays to assess their potency for the A2 compared to A1 adenosine receptor. The presence of an alpha-hydroxyl group in the alkynyl chain of NECA derivatives accounts for the A2 agonist potency, leading to compounds endowed with sub-nanomolar affinity in binding studies. However, these analogues also possess good A1 receptor affinity resulting in low A2 selectivity. From functional experiments the 4-hydroxy-1-butynyl (6) and the 4-(2-tetrahydro-2H-pyranyloxy)-1-butynyl (16) derivatives appear to be very potent in inducing vasorelaxation without appreciable effect on heart rate. The new compounds were also tested as inhibitors of platelet aggregation induced by ADP. Introduction of an alpha-hydroxyl group in the alkynyl side chain caused a greater increase in antiaggregatory activity than either NECA or HE-NECA, resulting in the most potent inhibitors of platelet aggregation so far known in the nucleoside series. The presence of an alpha-quaternary carbon such as the 3-hydroxy-3,5-dimethyl-1-hexynyl (12) and the 3-hydroxy-3-phenyl-1-butynyl (15) derivatives markedly reduced the antiaggregatory potency without affecting the A2 affinity. The hydrophobicity index (k') of the new nucleosides barely correlated with the binding data, whereas high k' values were associated with increased A2 vs A1 selectivity but with reduced activity in all functional assays. Some of the compounds synthesized possess interesting pharmacological properties. Compounds having an appropriate balance between vasorelaxation and antiplatelet activity, if confirmed in vivo, deserve further development for the treatments of cardiovascular disorders.

Adenosine deaminase inhibitors. Synthesis and biological activity of deaza analogues of erythro-9-(2-hydroxy-3-nonyl)adenine.

Two new deaza analogues of erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA, 1), 7-deaza-EHNA (6) and 1,3-dideaza-EHNA (11), were synthesized and evaluated for adenosine deaminase (ADA) inhibitory activity and compared with EHNA, 1-deaza-EHNA (2), and 3-deaza-EHNA (3). Substitution of a methine group for a nitrogen atom in the 7-position of the purine moiety of EHNA produces a dramatic drop in the inhibitory activity (Ki = 4 X 10(-4) M) whereas compounds 2 and 3 are still good inhibitors (Ki = 1.2 X 10(-7) M and 6.3 X 10(-9) M respectively). EHNA and its deaza analogues so far synthesized were also tested in vitro for their antiviral and antitumor activity in a range of cellular systems. EHNA and 1-deaza-EHNA are equiactive as inhibitors of human respiratory syncytial virus (HRSV) replication (MIC = 6.25 micrograms/mL) while the other compounds are inactive. On the other hand, all the examined compounds displayed an antitumor activity comparable to that of the reference compound 1-beta-D-arabinofuranosyladenine (ara-A), 7-deaza-EHNA being the most active of all. The results obtained showed that there is no correlation between adenosine deaminase inhibition and antiviral or antitumor activity in this series of compounds. 3-Deaza-EHNA, the most active inhibitor of ADA among the EHNA deaza analogues, greatly potentiates the antitumor activity of ara-A in vitro. In vivo activity was observed only when the two compounds were used in combination.

Synthesis and biological evaluation of N6-cycloalkyl derivatives of 1-deazaadenine nucleosides: a new class of anti-human immunodeficiency virus agents.

A series of 1-deazaadenine nucleosides with the N6 nitrogen unsubstituted or bearing methyl or cycloalkyl substituents, with or without a chloro group in the 2-position, and with the glycosylic moiety being ribose (1-16), 2'-deoxyribose (17-32), or 2', 3'-dideoxyribose (33-48) were designed and synthesized starting from 5,7-dichloro-3H-imidazo[4,5-b] pyridine (50). These compounds were evaluated for their in vitro activity against human immunodeficiency virus type-1 (HIV-1) and herpes simplex virus type-1 (HSV-1). In addition they were tested for their ability to inhibit adenosine deaminase (ADA) from calf intestine. While the parent compounds 1-deazaadenosine (9), 2'-deoxy-1-deazaadenosine (25), and 2',3'-dideoxy-1- deazaadenosine (41) and the corresponding 2-chloro derivatives were inactive, nucleosides bearing cycloalkyl substituents on N6 exhibited moderate to good anti-HIV-1 activity, compared to 2',3'-dideoxyadenosine, with the degree and pattern of improvement depending on the structure of the sugar moiety. In general, 2'-deoxy- and 2',3'-dideoxy derivatives were more potent compounds than the corresponding ribose nucleosides. Compounds bearing a 6-cycloheptyl or cyclooctylamine were the most active in every series. The presence of a chloro group in the 2-position improved both activity and therapeutic index in every series, the most active compound being 2'-deoxy-2-chloro-N6-cycloheptyl-1-deazaadenosine (23; ED50 = 0.2 microM). On the other hand, most of these derivatives were inactive as anti-HSV-1 agents, showing a high degree of virus selectivity. The 1-deazaadenine derivatives were not substrates of adenosine deaminase, and some of them proved to be good inhibitors of the enzyme. However, the ADA inhibitory activity does not account for the antiviral potency since increased lipophilicity and steric hindrance of substituents resulted in derivatives much less active than the parent compounds.

2-Aralkynyl and 2-heteroalkynyl derivatives of adenosine-5'-N-ethyluronamide as selective A2a adenosine receptor agonists.

A series of new 2-aralkynyl and 2-heteroaralkynyl derivatives of NECA were synthesized and studied in binding and functional assays to assess their potency for the A2a compared to A1 adenosine receptors. Compounds bearing an aromatic or heteroaromatic ring, conjugated to the triple bond, showed generally weaker activity at the A2a receptor and lower selectivity (A2a vs A1) than the alkylakynyl derivatives previously reported. However, the (4-formylphenyl)-ethynyl derivative 17 showed affinity in the low nanomolar range and high selectivity (about 160-fold) for the A2a receptor. The presence of heteroatoms improved vasorelaxant activity, the 2-thiazolylethynyl derivative 30 being the most potent in the series. Introduction of methylene groups between the triple bond and the phenyl ring favored the A2a binding affinity, and the 5-phenyl-1-pentynyl derivative 24 was found to be highly potent and selective (about 180-fold) at A2a receptors. With regard to antiplatelet activity, the presence of aromatic or heteroaromatic rings decreased potency in comparison with that of NECA and of N-ethyl-1'-deoxy-1'-(6-amino-2-hexynyl-9H-purin-9-yl)-beta-D-ribofura nuronamide (HENECA). Introduction of a methylene group was effective in increasing antiaggregatory potency only when this group is linked to a heteroatom (31-35). From these data and those previously reported, the structure-activity relationships derived for the 2-alkynyl-substituted ribose uronamides would indicate that potentiation of A2a receptor affinity could be obtained by aromatic rings not conjugated with the triple bond or by heteroaromatic groups. As for A2a receptors on platelets, the presence of aromatic rings, either conjugated or unconjugated to the triple bond, is detrimental for the antiaggregatory activity. However, the introduction of polar groups alpha to the triple bond strongly increases the potency when steric hindrance is avoided. Some of the compounds included in this series retain interesting vasodilating properties and merit further investigation for their potential in the treatment of cardiovascular disorders.

2-alkenyl and 2-alkyl derivatives of adenosine and adenosine-5'-N-ethyluronamide: different affinity and selectivity of E- and Z-diastereomers at A2A adenosine receptors.

A series of new 2-(ar)alkenyl, both Z- and E-diastereomers, and 2-alkyl derivatives of adenosine-5'-N-ethyluronamide (NECA) and adenosine were synthesized and evaluated for their interaction with the A1 and A2A adeosine receptors, to better understand the conformational requirements of the receptor area interacting with the substituents in the 2- and 5'-positions. Partial reduction of the triple bond in 2-alkynyl derivatives of NECA led to compounds whose activity at the A2A receptor subtype was related to Z-E-isomerism, the E-diastereomers being more potent and selective than the Z-ones. Saturation of the side chain markedly reduced compound affinity at adenosine receptors. Specifically, compounds bearing an (E)-alkenyl chain, while maintaining the same affinity at A2A receptors as the corresponding alknyl derivatives, showed an increase in A2A vs A1 selectivity. Hence, the new nucleosides (E)-2-hexenylNECA (12a) and (E)-2-(phenylpentenyl)NECA (12b) exhibited both high A2A receptor affinity (Ki = 1.6 and 3.5 nM, respectively) and A2A vs A1 selectivity (157- and 290-fold, respectively). Moreover, 12a displayed potent antiaggregatory activity, similar to that of the reference compound NECA. Comparison between NECA and adenosine derivatives further demonstrated that the 5'-ethylcarboxamido group is critical for the A2A affinity. These studies indicated that the orientation of the substituent in the 2-position and the nature of the 5'-group in adenosine derivatives are critical to achieve high affinity and selectivity at the A2A adenosine receptor subtype.

N-cycloalkyl derivatives of adenosine and 1-deazaadenosine as agonists and partial agonists of the A(1) adenosine receptor.

A number of cycloalkyl substituents (from C-3 to C-8) have been introduced on the 6-amino group of adenosine, 1-deazaadenosine, and 2'-deoxyadenosine, bearing or not a chlorine atom at the 2-position, to evaluate the influence on the A(1) and A(2A) affinity of steric hindrance and lipophilicity. Furthermore, the guanosine 5'-triphosphate (GTP) shift and the maximal induction of guanosine 5'-(gamma-thio)triphosphate ([(35)S]GTPgammaS) binding to G proteins in rat brain membranes were used to determine the intrinsic activity of these nucleosides at the A(1) adenosine receptor. All compounds of the ribose-bearing series proved to be full agonists, the 1-deaza derivatives showing affinities for the A(1) receptor about 10-fold lower than the corresponding adenosines. On the other hand, all the 2'-deoxyribose derivatives bind to the A(1) receptor with affinities in the high nanomolar range, with the 2-chloro substituted compounds showing slightly higher affinities than the 2-unsubstituted counterparts. In terms of the potencies, the most potent compounds proved to be those bearing four- and five-membered rings. Both GTP shifts and [(35)S]-GTPgammaS experiments showed that most of the 2'-deoxyadenosine derivatives are partial agonists. The 2'-deoxyadenosine derivatives which were identified as partial agonists consistently detected fewer A(1) receptors in the high-affinity state than full agonists. However, it is worthwhile noting that there was not a simple linear relationship between receptor occupancy and activation. These results indicate that a critical density of A(1) adenosine receptors in the high-affinity state is required for G protein activation.

Synthesis and biological activity of a new series of N6-arylcarbamoyl, 2-(Ar)alkynyl-N6-arylcarbamoyl, and N6-carboxamido derivatives of adenosine-5'-N-ethyluronamide as A1 and A3 adenosine receptor agonists.

A new series of 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-beta-D-ribofuranuronamide++ +-b earing N-arylureas or N-arylcarboxamido groups at the purine 6 position and N-arylureas combined with halogens or alkynyl chains at the 2 position have been synthesized and tested for affinity at A1 and A2A adenosine receptors in rat brain membranes and at cloned rat A3 receptors expressed in CHO cells. The derivatives contained the 5' substituent found in the potent, nonselective agonist 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-beta-D-ribofuranuronamide++ + (NECA). While the carboxamido derivatives (9-13) showed affinity for A1 receptors, the urea derivatives (30-45) showed different degrees of affinity and selectivity for the A3 adenosine receptor subtype. In particular the derivative bearing a p-sulfonamidophenyl-urea at the 6 position, 31 showed a high affinity (Ki = 9 nM) and selectivity for the A3 receptors compared to that of the reference compound 1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-be ta-D-ribofuranuronamide (IB-MECA). Furthermore, the importance of the stereochemistry in the interaction of these ligands at the rat A3 adenosine receptors has been evaluated by introducing a chiral chain at the 6 position. The introduction of halogens or alkynyl chains at the purine 2 position of selected ureas did not give the expected enhancement of potency at A2A and/or A3 receptors but rather showed a dramatic reduction of A2A affinity, resulting in compounds with good A2A/A3 selectivity. For example, the 2-(3-hydroxy-3-phenyl-1-propyn-1-yl)-6-(4-methoxyphenylurea) derivative 61 showed the capability to bind simultaneously to A1 and A3 receptor subtypes, excluding the A2A receptor. Compound 31 was shown to be an agonist, 9-fold more potent than NECA, at A3 receptors in rat RBL-2H3 mast cell membranes through stimulation of binding of [35S]GTP-gamma-S.