Biosynthesis and cytokinin activity of 8-hydroxy and 2,8-dihydroxy derivatives of zeatin and N-6(increment-2-isopentenyl)adenine.

8-Hydroxy and 2,8-dihydroxy derivatives of the cytokinins, 6-(4-hydroxy-3-methyl-trans-2-butenylamino)purine and N-6-(increment -2-isopentenyl)adenine, have been biosynthesized by xanthine oxidase oxidation. 8-Hydroxy derivatives have been shown to be the major intermdeiates. These compounds were tested for cytokinin activity in the tobacco bioassay. The results suggest that substitution of the 8 position with a hydroxyl group causes less decrease of cytokinin activity than substitution of both the 2 and 8 positions with hydroxyl groups.     

Cytokinins with different connecting links between purine and isopentenyl or benzyl groups

Using the tobacco bioassay a comparison was made between the cytokinin activities of the following series of compounds with different connecting links (6-NH, S, O, CH₂) between the purine ring and isopentenyl or benzyl groups: 6-(3-methyl-2-butenylamino)purine (1a), 6-(3-methyl-2- butenylthio)purine (1b), 6-(3-methyl-2-butenyloxy)purine (1c), and 6-(4-methyl-3-pentenyl)purine (1d); 6-benzylaminopurine (2a), 6-benzylthiopurine (2b), 6-benzyloxypurine (2c), and 6-(2-phenethyl)purine (2d); also 6-trans-styrylpurine (3), the synthetic precursor of 2d. All possess cytokinin activity, thus providing evidence that the intact base, consisting of nucleus and sidechain at the purine 6-position, is necessary and sufficient for such activity as measured in the tobacco bioassay. The biological activity in the 6-(3-methyl- 2-butenyl-X)purine series decreases as a function of the linkage group in the order X = NH > CH₂ > S ⪢ O and in the 6-benzyl-X-purine series in the order X = NH > CH₂ = O ⪢ S. The 6-trans-styrylpurine (3) is about equally active as 6-(2-phenethyl)purine (2d).     

Impact of hydroxy moieties at the benzo[7]annulene ring system of GluN2B ligands: Design,synthesis and biological evaluation

In this study, the impact of one or two hydroxy moieties at the benzo[7]annulene scaffold on the GluN2B affinity and cytoprotective activity was analyzed. The key intermediate for the synthesis of OH-substituted benzo[7]annulenamines 11–13 and 17 was the epoxyketone 8. Reductive epoxide opening of 8 resulted with high regioselectivity in the 5-hydroxyketone 9 (Pd(OAc)₂, HCO₂H, phosphane ligand) or the 6-hydroxyketone 10 (H₂, Pd/C), whereas hydrolysis in aqueous dioxane led to the dihydroxyketone 14. Reductive amination of these ketones with primary amines and NaBH(OAc)₃ afforded the benzo[7]annulenamines 11–13 and 17. In receptor binding studies 5-OH derivatives 11 and 12 showed higher GluN2B affinity than 6-OH derivatives 13, which in turn were more active than 5,6-di-OH derivative 17a. The same order was found for the cytoprotective activity of the ligands. The tertiary amine 12a with one OH moiety in 5-position represents the most promising GluN2B negative allosteric modulator with a binding affinity of K_i = 49 nM and a cytoprotective activity of IC₅₀ = 580 nM. In the binding pocket 12a shows a crucial H-bond between the benzylic OH moiety and the backbone carbonyl O-atom of Ser132 (GluN1b). It was concluded that a 5-OH moiety is essential for the inhibition of the NMDA receptor associated ion channel, whereas a OH moiety in 6-position is detrimental for binding and inhibition. An OH or CH₂OH moiety at 2-position results in binding at the ifenprodil binding site, but very weak ion channel inhibition.     

Triaryl (Z)-olefins suitable for radiolabeling with carbon-11 or fluorine-18 radionuclides for positron emission tomography imaging of cyclooxygenase-2 expression in pathological disease

A group of (Z)-1,1-diphenyl-2-(4-methylsulfonylphenyl)alk-1-enes were synthesized using methodologies that will allow incorporation of a [¹¹C]OCH₃ substituent at the para-position of the C-1 phenyl ring, a [¹¹C]SO₂CH₃ substituent at the para-position of the C-2 phenyl ring, a [¹⁸F]OCH₂CH₂F substituent at the para-position of the C-1 phenyl ring, and a [¹⁸F]CH₂CH₂F substituent at the C-2 position of the olefinic bond. The [¹¹C] and [¹⁸F] radiotracers are designed as potential radiopharmaceuticals to image cyclooxygenase-2 (COX-2) expression in any organ where COX-2 is upregulated. The COX-1/COX-2 inhibition data acquired suggest that compounds having a [¹¹C]OMe or [¹⁸F]OCH₂CH₂F substituent at the para-position of the C-1 phenyl ring may be more suitable for imaging COX-2 expression in view of their ability to exclusively inhibit the COX-2 isozyme.     

Benzofuran- and furan-2-yl-(phenyl)-3-pyridylmethanols: Synthesis and inhibition of P450 aromatase

A series of benzofuran-2-yl-(phenyl)-3-pyridylmethanol derivatives were prepared using an efficient 1-step procedure in good yields. In addition furan-2-yl-(phenyl)-3-pyridylmethanol derivatives were also prepared to determine the effect of the benzene ring in benzofuran with respect to inhibitory activity. The pyridylmethanol derivatives were all evaluated in vitro for inhibitory activity against aromatase (P450_AROM, CYP19), using human placental microsomes. The benzofuran-2-yl-(phenyl)-3-pyridylmethanol derivatives showed good to moderate activity (IC₅₀=1.3–25.1?μM), which was either better than or comparable with aminoglutethimide (IC₅₀=18.5?μM) but lower than arimidex (IC₅₀=0.6?μM), with the 4-methoxyphenyl substituted derivative displaying optimum activity. Molecular modelling of the benzofuran-2-yl-(4-fluorophenyl)-3-pyridylmethanol derivative suggested activity to reside with the (S)-enantiomer. The furan-2-yl-(phenyl)-3-pyridylmethanol derivatives were devoid of activity indicating the essential role of the benzene ring of the benzofuran component for enzyme binding.     

Synthesis and Biological Activity of Trisubstituted Adenines as A 2A Adenosine Receptor Antagonists

The discovery of new drugs for the treatment of neurodegenerative disorders, such as Parkinson's disease, has become an attractive field of research. Due to the regulation of D ₂ receptor activity by A _{2 A} adenosine receptor, potent and selective ligands of A _{2 A} subtype could be useful tools to study neurodegenerative disorders. A series of 2,8-disubstituted-9-ethyladenine derivatives was synthesized and tested in binding affinity assay at human adenosine receptors. New compounds showed good affinity and selectivity at A _{2 A} receptor versus the other subtypes. The introduction of a bromine atom in 8-position increased the affinity of these compounds, leading to ligands with K _i in the nanomolar range.     

The alkenic unreactivity of mono- and bi-cyclic derivatives of 3,6-dihydro-2-(methylthio)-2H-thiopyran S,S,S′,S′-tetraoxide

The inertness of the alkenic bond towards electrophilic additions in 3-exocyano-3-(methylthio)-2-thiabicyclo[2.2.1]hept-5-ene S,S,S′,S′-tetraoxide (5), 3,6-dihydro-2-(methylthio)-2H-thiopyran-2-carbonitrile S,S,S′,S′-tetraoxide (3), and 2-(acetamidomethyl)-3,6-dihydro-2-(methylthio)-2H-thiopyran S,S,S′,S′-tetraoxide (4) is attributed to the “supra-annular effect” and field effects. Conformational analysis of a pentadeuterated derivative of 4 (10) is reported. On the basis of the 220-MHz ¹H n.m.r.-spectral data of 10, the compound was concluded to adopt the ⁰H₂ conformation in chloroform solution.     

Syntheses of 6-(2-hydroxy-6-phenylhexyl)-5,6-dihydro-2H-pyran-2-one derivatives and their cytotoxicities

The cytotoxicities against cancer cells (HL-60, HeLa) and insect cells (Sf9) of four stereoisomers of 6-(2-hydroxy-6-phenylhexyl)− 5,6-dihydro-2H-pyran-2-one (1) were evaluated, and then their structure-activity relationships examined. The 2′-dehydroxy derivative 5 of (6 R,2′R)- and (6 R,2′S)-1 showed the highest activity against HeLa cells (IC₅₀ = 1.4 μM). To evaluate the effect of the 2′-hydroxy group of 1, 6R-and 6S-oxetane derivatives were also synthesized and their activities examined. Against HeLa and HL-60 cells, the activities of the less potent stereoisomers were enhanced 3–4-fold by the introduction of the oxetane moieties at the 2′-position. Against the insect cell line (Sf9), phenyl derivative 7 showed the highest activity with an IC₅₀ value of 8.0 μM.     

Synthesis,cytotoxic activity,DNA topoisomerase-II inhibition,molecular modeling and structure–activity relationship of 9-anilinothiazolo[5,4-b]quinoline derivatives

Some novel 9-anilinothiazolo[5,4-b]quinoline derivatives were synthesized and their cytotoxic activities were examined. The inhibition of some of the most active compounds over human topoisomerase II (Topo II) activity was assessed with the kDNA decatenation assay. The novel compounds differ in the substituents attached to the anilino ring, a dialkylamino alkylamino group, a saturated heterocyclic moiety, a methylthio group at position 2 and a fluorine atom present or absent at 7-position. According to the data, compounds with a diethylaminopropylamino group and a chlorine atom at 4′-position of the anilino ring were the most cytotoxic. The molecular models of all compounds indicated a correlation between hydrophobicity and cytotoxic activity although the direction and magnitude of the dipole moment also had a significant influence on its cytotoxicity. The 2-dialkylaminoalkylamino substituent is flexible and is known to facilitate the crossing of cell membranes; thus, this last barrier may be a limiting step in the mechanisms mediating the cytotoxicity. On the other hand, the activity of 2-methylthio derivatives seems to rely more on the electronic effects brought about by the substitution of the aniline ring. The synthesis, cytotoxicity against cancer cell lines, in vitro inhibition of human topoisomerase II, molecular modeling and the preliminary analysis of structure–activity relationships are presented.     

Design,synthesis and anti-P. falciparum activity of pyrazolopyridine–sulfonamide derivatives

Ten 1-phenyl-1H-pyrazolo[3,4-b]pyridine derivatives connected by a linker group to benzenesulfonamide moieties with different substituents in the 4-position were synthesized and assayed against Plasmodium falciparum. These ten compounds exhibited activity in vitro against the chloroquine-resistant clone W2 with IC₅₀ values ranging from 3.46 to 9.30 μM. The most active derivatives with substituent R₂ = Cl or CH₃ at the benzenesulfonamide moiety exhibited the lowest IC₅₀. Compounds with an R₁ = CO₂Et substituent at the 5-position of the 1H-pyrazolo[3,4-b]pyridine ring presented lower activity than those with a CN substituent. The 1H-pyrazolo[3,4-b]pyridine system appears to be promising for further studies as an antimalarial for overcoming the burden of resistance in P. falciparum.     

Inhibitory effect of 8-substituted adenosine derivatives on Ca++ and modulator protein-dependent phosphodiesterase activity.

8-Substituted adenosine and cyclic AMP derivatives exhibited some negative Cotton effects in circular Dichroism at B_2u band in pH 7.5 solution, suggesting that these derivatives take syn conformation. The adenosine derivatives, as well as cyclic AMP derivatives, competitively inhibited the cyclic AMP hydrolyzing activity in Ca⁺⁺ and modulator protein-dependent phosphodiesterase preparation from hog brain cortex. The inhibitory potential of an adenosine derivative was lower than that of the cyclic AMP derivative having the same substituent by the lack of the phosphate moiety for which affinity was 0.5 kcal / mol. These results may suggest that the cyclic AMP hydrolyzing site on the enzyme requires the syn conformation of purine riboside.     

8-Substituted 2-alkynyl-N9-propargyladenines as A2A adenosine receptor antagonists

Structure–activity relationships of 2-alkynyladenine derivatives were explored by varying substituents at the 9-, 8- and 2-positions of the purine moiety in order to optimize A_2A adenosine receptor antagonist activity in vitro. A propargyl group at the 9-position was found to be important for A_2A antagonist activity, and the introduction of a halogen, aryl, or heteroaryl at the 8-position further enhanced activity. A series of 8-substituted 2-alkynyl-N⁹-propargyladenine derivatives exhibited potent antagonist activity, with IC₅₀ values in the low nM range. Compound 4a from this series was found to be orally active at a dose of 3 mg/kg in a mouse catalepsy model and a 6-hydroxydopamine-lesioned rat model of Parkinson’s disease.     

Inhibitors of the tissue factor/factor VIIa-induced coagulation: synthesis and in vitro evaluation of novel specific 2-aryl substituted 4H-3,1-benzoxazin-4-ones

The synthesis of a series of novel 2-aryl substituted 4H-3,1-benzoxazin-4-ones and their evaluation as specific inhibitors of the Tissue Factor (TF)/Factor VIIa (FVIIa)-induced pathway of coagulation is reported. Inhibitory activities (IC50 values) in the range 0.17 to > 40 microM on the activation of Factor X (FX) by the TF/FVIIa complex were found for compounds having one or two electronegative substituents such as F, Cl and NO2 in the 2-aryl substituent. Different substitutions both electron-attracting and donating groups were allowed in the 5, 6, 7 and 8 positions. Several of the compounds showed a selectivity ratio towards FX and thrombin of > 50, thus being the first small molecules described as potential drugs for oral antithrombotic treatment without side effects such as bleeding which is observed especially with thrombin inhibitors. The best substituent pattern being the 2-aryl group substituted with: 2-F; 2,6-F2; or 2-FX; 6-Cl; together with electronegative substitution in the 5, 6, 7, or 8 positions. 2-Heteroaryl substituents like thienyl and furanyl were of low activity while some 2-(2-chloro-3-pyridyl) derivatives had inhibitory activity < 10 microM and a good selectivity.     

2-Arylmethylaminomethyl-5,6-dihydroxychromone derivatives with selective anti-HCV activity

Anti-HCV activity of aryl diketoacid (ADK) has been characterized by its two pharmacophoric elements, α,β-diketo acid moiety and substituted aryl ring. In this study, as a part of our ongoing efforts to discover a novel anti-HCV compound mimicking the ADK scaffold, we designed 2-arylmethylaminomethyl-5,6-dihydroxychromone derivatives of which the dihydroxychromone moiety as well as the arylmethylaminomethyl substituent (R-PhCH₂NHCH₂-) were anticipated in exact match with the pharmacophore model of the ADK. The dihydroxychromone derivatives (3a-3u), thus prepared, showed biological activity in a substituent-dependent fashion, thereby leading to selective anti-HCV effect (EC₅₀ = 2.0-14.0 μM, CC₅₀ >100 μM) with the substituent groups such as Cl, Br, I, and Me specifically at the 3-position of the aromatic ring.     

Synthesis and antiviral activity of 1-(1,3-disubstitutedimidazolidyn-2-ylidene)-3-ethoxycarbonylmethylurea derivatives

Novel 1-(1,3-disubstituted-imidazolidyn-2-ylidene)-3-ethoxycarbonylmethylurea derivatives (3a–3j) were obtained from appropriate 1-aryl-3-arylsulfonyl-1H-imidazolidine-2-imines (1a–1j) and ethyl isocyanatoacetate (2), which were subjected to condensation. Seven compounds were tested for their antiviral activity against HSV-1 and CVB3 viruses. Among the tested compounds, 3c was found to be active against HSV-1, proving that 4-methoxy substituent as R and 4-methyl substituent as R₁ are most beneficial for activity against this virus. Furthermore, 3e and 3g were active against CVB3, which demonstrated that both 4-methyl and 4-chloro substitution is tolerated as R₁, whereas 4-chloro and 2-methoxy substituents are best as R. It was also shown that the active compounds are characterized by relatively big surface area, small ovality, and greatest HOMO and LUMO energies in comparison to the rest of the compounds.     

Synthesis and Antitumor Activity of 2-Alkanesulfinyl (or Alkanesulfonyl)-7-methyl-5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-ones

The repressing effect on the propagation of cultured Ehrlich ascites tumor cells by 1, 3, 4-thiadiazolo [3, 2-a] pyrimidine and s-triazolo [1, 5-a] pyrimidine derivatives was examined. Then the relationship between structure and activity as to a series of active compounds was discussed.

The results showed that substituent groups on the 2-position of 1, 3, 4-thiadiazolo [3, 2-a]-pyrimidine took an important part to reveal the cytotoxic activity. Especially, the strong activity was found among the compounds which had electrophilic substituents such as alkylsulfoxide, alkylsulfone at the 2-position.     

Cytokinin-agonistic and antagonistic activities of 4-substituted-2-methylpyrrolo[2,3-d] pyrimidines, 7-deaza analogs of cytokinin-active adenine derivatives

Sixteen 4-substituted-2-methylpyrrolo[2,3-d]pyrimidines were tested for their activities as cytokinin agonists and antagonists in three bioassay systems. With the systematic variation of the 4-substituent, the activity changed consecutively from agonistic to antagonistic in the tobacco callus test, and this agonist-antagonist relationship was analysed by a steric substituent parameter as a common quantitative measure. Two compounds were found to possess bud-forming activity in the absence of added cytokinins. Eight compounds promoted betacyanin synthesis'in Amaranthus and 4 promoted germination in lettuce seeds. The 4-hydroxyethyl derivative, which was inactive in the tobacco test, suppressed betacyanin synthesis at 100 μM against 100 μM 6-(3-methyl-2-butenylamino)- purine. The 4-phenyl derivative showed antagonist activity in the tobacco test, little activity in the Amaranthus bio- assay and significant agonist activity in the lettuce seed germination. The 4-cyclobutyl derivative exerted the strongest anticytokinin activity (I₅₀ at 0.06 μM against 0.05 μM kinetin) in the tobacco callus assay, while little activity was observed in the other two assay systems.     

Quantitative structure–activity relationship study of new potent and selective antagonists at the 5-HT1A and adrenergic α1d receptors: Derivatives of spiroethyl phenyl(substituted)piperazine

The antagonistic activities of derivatives of spiroethyl phenyl(substituted)piperazine at the 5-HT_1A and adrenergic α_1d receptors is quantitatively analyzed employing physicochemical and structural parameters. The derived correlation equation revealed that a substituent, other than 2-CH₃ in the phenyl ring, having higher molar refraction, MR, and a substituent producing higher positive field effect at the 3-position are beneficial in increasing the binding affinity at the 5-HT_1A receptor. In addition, a less hydrophobic substituent at the 4-position is also helpful in augmenting the binding affinity. The 5-R substituents which have higher MR values, however, elicit a detrimental effect. Two disubstituted compounds which are not present in the original data-set and have higher theoretical binding affinities are designed from the correlation equation. These compounds consisting of 2-OCH(CH₃)₂, 3-Cl and 2-C₃H₇, 3-Cl in the phenyl ring, have theoretical pK_i values 10.57 and 10.12 respectively. For the adrenergic α_1d receptor, a less bulky group at the 3-position with 5-Cl (or simply a 3-Cl) is advantageous in increasing the binding affinity. Likewise, a substituent exhibiting a less negative resonance effect at the 4-position and the substituent with low polarizability and showing more a negative resonance effect at the 5-position are suitable for enhancement of the binding affinity. The analysis provides the grounds for rationalizing substituent selection in designing better potency antagonists in the series.     

The cytokinin activities of 6-α-alkylbenzyloxypurines

The homologous series of 6-α-n-alkylbenzyloxypurines with alkyl groups (—(CH₂)_nCH₃) from n = 0 to n = 11 have been prepared and examined in three tests for cytokinin activity. The parent benzyloxypurine was also included in the tests. Substituting methyl (n = 0) into the methylene group of 6-benzyloxypurine removed activity almost completely; thereafter, increasing the size of the alkyl group (n = 1–5) gave compounds which were active in all tests, the butyl (n = 3) and pentyl (n = 4) derivatives being more active than 6-benzyloxypurine itself. Activity then fell as the series was ascended; the higher homologues (n = 8–11) being completely inactive. The results are discussed in relation to steric and other considerations.