Synthesis and phosphodiesterase inhibitory activity of new sildenafil analogues containing a carboxylic acid group in the 5'-sulfonamide moiety of a phenyl ring

New sildenafil analogues possessing a carboxylic acid group in the 5'-sulfonamide of the phenyl ring, 9a-l, were prepared from the readily available starting compounds 6a-b and cyclic amines 3-5 in a three-step sequence. In the enzyme assays, it has been shown that all the target compounds 9a-l proved to be more potent in inhibiting phosphodiesterase type 5 (PDE5) than sildenafil by 4-38-fold. The effects on the IC(50) values were investigated by varying the alkoxy group (R) of the phenyl ring, the sulfonamide type (X), and the length of the methylene chain linking the carboxylic acid, and the results were discussed in detail. From this study, we have clearly demonstrated that introduction of a carboxylic acid group to the 5'-sulfonamide moiety of the phenyl ring greatly enhanced PDE5 inhibitory activity, probably by mimicking the phosphate group of cGMP. The piperidinyl propionic acid derivative 9i, which showed the highest PDE5 inhibitory activity and comparable to better selectivity over PDE isozymes in comparison with sildenafil, has been selected for more detailed biological investigations.     

Synthesis and phosphodiesterase 5 inhibitory activity of new sildenafil analogues containing a phosphonate group in the 5(')-sulfonamide moiety of phenyl ring

Synthesis of new sildenafil analogues containing a phosphonate group in the 5(')-sulfonamide moiety of the phenyl ring, 12a-e, 13a-d, and 14a-d, and evaluation of their in vitro PDE5 inhibitory activity are disclosed. Enzyme assays revealed that maximum 10-fold increase in PDE5 inhibitory activity, compared with sildenafil, was achieved by introducing a phosphonate group in the 5(')-sulfonamide moiety. Docking model of (PDE5: 12d) complex shows that the PDE5-bound conformation of 12d matches completely with that of sildenafil, while 12d is partially overlapped with cGMP with ethyl phosphonate group of 12d superimposed onto the cyclic phosphate group of cGMP.     

Synthesis and phosphodiesterase 5 inhibitory activity of new 5-phenyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one derivatives containing an N-acylamido group phenyl ring.

New sildenafil analogues with an N-acylamido group at the 5'-position of the phenyl ring, 6a--e, were prepared from the readily available starting compound 2 in four straightforward steps. Enzyme assays demonstrated that all the target compounds 6a-e showed higher PDE5 inhibitory activities than sildenafil. It was observed that the PDE5 inhibitory activity was enhanced as the chain length of R group increased, but introduction of the branched alkyl groups such as isopropyl (6d) and cyclohexyl (6e) resulted in the drop of potency compared with 6c. In particular the N-butyrylamido derivative 6c exhibited the highest PDE5 inhibitory activity, and was about 6-fold more potent than sildenafil. However, all the compounds exhibited somewhat weak selectivity (1--3-fold) over PDE6, indicating that the compounds 6a--e have intrinsically lower selectivity than sildenafil.     

Syntheses of 4,6'-epoxymorphinan derivatives and their pharmacologies

A modification of the message site in the skeleton of naltrexone was carried out to improve the potency and selectivity of the compound for an opioid receptor subtype. In the course of conversion, we synthesized 7-membered ring ether derivatives, which had an inserted OCH(2) group between 4- and 6-positions of morphinan skeleton. One of the 7-membered ring ether derivatives possessed more potent antagonistic activity than naltrexone for the mu opioid receptor. Another compound possessing 17-methyl group derived from noroxycodone may be a mu opioid receptor partial agonist and showed analgesic activity. We are currently examining the subtype selectivity of these compounds.     

Herbicidal aryldiones incorporating a 5-methoxy-[1,2,5]triazepane ring

Novel 2-aryl-cyclic-1,3-diones containing a 5-methoxy-[1,2,5]triazepane unit were explored towards an effective and wheat safe control of grass weeds. Their preparation builds on the ease of synthetic access to 7-membered heterocyclic [1,2,5]triazepane building blocks. Substitution and pattern hopping in the phenyl moiety revealed structure–activity relationships in good agreement with previously disclosed observations amongst the pinoxaden family of acetyl-CoA carboxylase inhibitors. In light of basic physicochemical, enzyme inhibitory and binding site properties, the N-methoxy functionality effectively acts as a bioisostere of the ether group in the seven-membered hydrazine ring.     

Nucleosides. IX. Synthesis of purine N(3),5'-cyclonucleosides and N(3),5'-cyclo-2',3'-seconucleosides via Mitsunobu reaction as TIBO-like derivatives

The Mitsunobu reaction was applied to prepare, in one step, purine N(3),5'-cyclonucleosides 10a-d. A subsequent ring opening in the ribose moiety of the resultant N(3),5'-nucleosides by sodium periodate led to the corresponding N(3),5'-cyclo-2',3'-seconucleosides. These products consist of 5-, 6-, and 7-membered tricyclic system which is the basic skeleton of TIBO derivatives, known antiviral agents.     

Molecular modeling study of 4-phenylpiperazine and 4-phenyl-1,2,3,6-tetrahydropyridine derivatives: A new step towards the design of high-affinity 5-HT1A ligands

The main feature of many drugs having a 5-HT_1A affinity is the presence of an arylpiperazine moiety. Indeed, the protonated nitrogen and the aromatic ring of the arylpiperazine compounds are considered crucial for the interaction with the receptor. However, the replacement of the piperazine moiety by a 1,2,3,6-tetrahydropyridine ring in 4-arylpiperazine-ethyl carboxamide derivatives was recently shown to be highly favourable for 5-HT_1A affinity. In order to better understand the favourable effect of this chemical modification, we performed a conformational analysis of these compounds mainly based on the position of the phenyl ring relative to the piperazine and tetrahydropyridine moiety. In the piperazine compounds, the phenyl ring preferentially adopts a perpendicular orientation, whereas an almost planar orientation seems to be the most favourable conformation for the tetrahydropyridine compounds. Therefore, this conformational difference appears as a key for a better interaction with the receptor binding site. This result will serve for the designing high-affinity 5-HT_1A ligands.     

Chiral derivatives of 2-(1-naphthyl)-2-phenylacetic acid

The spectral properties of diastereomeric esters and amides (1b-20b), derived from optically pure 2-(1-naphthyl)-2-phenylacetic acids (1-NPA), were systematically investigated. It was found that all compounds prepared exhibit the NMR spectral nonequivalence (Deltadelta) with regular sign distribution of particular groups according to the predicted model. Further, the analysis of data revealed that the phenyl ring is responsible for a shielding effect (upfield shift) instead of a naphthyl one. This conclusion is supported by the crystallographic analysis showing the almost ap-arrangement of the acid methine hydrogen atom and carbonyl group. In this arrangement, the phenyl ring faces toward the ester part of the molecule while the naphthyl one is orthogonal to the phenyl plane. Therefore, the mutual position of phenyl and alkyl groups with respect to the central molecule co-planarity thus determines the chemical shifts of the alcohol/amine substituents. The relative magnitude of the Deltadelta corresponds to those of Mosher's derivatives.     

Synthesis and cytotoxic evaluation of new (4,5,6,7-tetrahydro-indol-1-yl)-3-R-propionic acids and propionic acid ethyl esters generated by molecular mimicry

Indolones 4 and 5, and indolyl-aminoacids 6a-e, 7a-e, and 8a and 8b were designed by structural modification of lead compound 3. These compounds were tested on six tumor cell lines to determine the role of the azepinone ring and the N-phenyl substituent in the cytotoxicity of 3. Our results show that 4 and 5 have dramatically reduced cytotoxicity, due to the loss of the azepinone moiety of lead compound 3. In contrast, indolyl-aminoacids 6a, 7a, and 8a (N-(L)-cysteine ethyl ester derivatives) inhibited the proliferation of almost all cancer cell lines tested, even though they lack the azepinone ring. In addition, derivative 6c (N-(D)-alanine methyl ester group) was selectively cytotoxic to HCT-15 cells. Preliminary structure-activity relationship (SAR) studies with these compounds revealed the importance of the ethyl ester moiety on the amino acid moiety. Compounds 6a-e, 7a-e, and 8a and 8b were obtained in good yields by a catalytic Paal-Knorr reaction carried out under microwave irradiation using commercially available chiral amino esters or amino acids and 1,4-dicarbonyl compounds.     

New steroid-fused P-heterocycles. Part I. Synthesis and conformational study of dioxaphosphorino[16,17-d]estrone derivatives

D-ring-fused dioxaphosphorinanes (4-6) in the estrone series were synthetized as epimeric pairs and investigated by NMR and computational methods in order to determine their stereostructures and predominant conformations. The study was performed to evaluate the influence of the rigid sterane framework on the geometry of the condensed hetero ring, with regard to the possible steric effect of the angular methyl group at position 13. Additionally, the steric and electronic effects of the P-substituents on the conformational equilibrium were examined. The distorted-boat conformation of the hetero ring of dioxaphosphorinoestrone 3-methyl ether 4a was confirmed by single-crystal X-ray analysis. This is in good agreement with the observation in solution that, in the case of the boat conformation, the anisotropic shielding effect of the phenyl group of cyclic phosphonate 4a generates an upfield shift for 17-H, as compared with the corresponding chemical shift for epimer 4b. A similar boat conformation was substantiated for derivatives 4b, 5a, 5b and 6b on the basis of the J(H, H) and J(H, P) coupling constants and also ab initio calculations, regardless of the P-configuration. At the same time, the hetero ring of 6a seems to tilt towards a chair-like conformation due to the strong equatorial preference of the N-bis(2-chloroethyl) group.     

Alicyclic β-amino acids in Medicinal Chemistry

Summary. The structural element of alicyclic β-amino acids shows some remarkable biological effects: For some 5- and 6-membered β-amino acids a unique anti fungal activity has been observed, 7-membered β-amino acid derivatives have been investigated for neurological disorders. The application of 5-, 6- and 7-membered alicyclic β-amino acids in Medicinal Chemistry will be reported.     

The effect of substitution patterns on the release rates of opioid peptides DADLE and [Leu(5)]-enkephalin from coumarin prodrug moieties

A coumarin-based prodrug system has been developed in our laboratory for the preparation of esterase-sensitive prodrugs of amines, peptides, and peptidomimetics. The drug release rates from this prodrug system were found to be dependent on the structural features of the drug moiety. The effect of the phenyl ring substitutions on the release kinetics of such prodrugs of model amines was examined recently and it was found that appropriately positioned alkyl substituents on the phenyl ring could help to facilitate the release. Aimed at further understanding the structure-release rate relationship of the coumarin-based cyclic prodrugs, we synthesized and examined a series of substituted coumarinic acid derivatives of opioid peptides, DADLE, and [Leu(5)]-enkephalin.     

Nucleosides and nucleotides. 192. Toward the total synthesis of cyclic ADP-carbocyclic-ribose. Formation of the intramolecular pyrophosphate linkage by a conformation-restriction strategy in a syn-form using a halogen substitution at the 8-position of the adenine ring

The synthesis of cyclic ADP-carbocyclic-ribose (2), as a stable mimic for cyclic ADP-ribose, was investigated. Construction of the 18-membered backbone structure was successfully achieved by condensation of the two phosphate groups of 19, possibly due to restriction of the conformation of the substrate in a syn-form using an 8-chloro substituent at the adenine moiety. SN2 reactions between an optically active carbocyclic unit 8, which was constructed by a previously developed method, and 8-bromo-N6-trichloroacetyl-2',3'-O-isopropylideneadenosine 9c gave N-1-carbocyclic derivative, which was deprotected to give 5'-5"-diol derivatives 18. When 18 was treated with POCl3 in PO(OEt)3, the bromo group at the 8-position was replaced to give N-1-carbocyclic-8-chloroadenosine 5',5"-diphosphate derivative 19 in 43% yield. Treatment of 19 with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride gave the desired intramolecular condensation product 20 in 10% yield. This is the first chemical construction of the 18-membered backbone structure containing an intramolecular pyrophosphate linkage of a cADPR-related compound with an adenine base.     

For-Met-Lys-Phe- For-Met-Lys-Phe-: A new cyclic analogue of the chemotactic formylpeptides

As a continuation of the studies on chemotactic N-formylpeptides, we report here the synthesis and activity of a new cyclic analogue of the prototypical ligand For-Met-Leu-Phe-OMe. The new compound contains a 20-membered cyclic moiety made up of a dimeric-Lys-Phe-sequence in which For-Met is attached to each Lys α-NH₂-and hence remains outside the ring. The conformation in the crystal of the cyclic precursor of 4 , namely and the activity of the structurally related linear analogue For-Met-Lys(Z)-Phe-OBzl ( 6 ), have also been examined. The new analogues 4 and 6 are active as chemoattractants, secretagogues and superoxide anion generating agents, when tested on human neutrophils. The structure-activity relationship is discussed and related to that of a previously studied cyclic model. © 1995 John Wiley & Sons, Inc.     

Synthesis,anti-thymidine phosphorylase activity and molecular docking of 5-thioxo-[1,2,4]triazolo[1,5-a][1,3,5]triazin-7-ones

In our lead finding program, a series of 5-thioxo-[1,2,4]triazolo[1,5-a][1,3,5]triazin-7-ones and their 5-thio-alkyl derivatives were designed and synthesized which contained different substituents at ortho-position of 2-phenyl ring attached to the fused ring structure. The preliminary pharmacological evaluation demonstrated that the synthesized compounds exhibited a varying degree of inhibitory activity towards thymidine phosphorylase (TP), comparable to reference compound, 7-Deazaxanthine (7-DX, 2) (IC₅₀ value = 42.63 μM). The study also inferred that the ortho-substituted group at the phenyl ring and 5-thio-alkyl moiety imparted steric hindrance effects in the binding site of the enzyme, leading to a reduced inhibitory response. In addition, compound 3a was identified as a mixed-type inhibitor of TP. Moreover, computational docking study was performed to illustrate the important structural information on the plausible ligand-enzyme binding interactions.     

The new generation dihydropyridine type calcium blockers, bearing 4-phenyl oxypropanolamine, display alpha-/beta-adrenoceptor antagonist and long-acting antihypertensive activities

A new series of dihydropyridine derivatives, bearing oxypropanolamine moiety on phenyl ring at the 4-position of the dihydropyridine base, were prepared. Oxypropanolamine was synthesized by replacing the phenolic OH of vanillin or other compounds, having a phenyl aldehyde group, with epichlorohydrin, followed by cleavaging the obtained epoxide compounds with tert-butylamine, n-butylamine or 2-methoxy-1-oxyethylamino benzene (guaiacoxyethylamine), respectively. Obtained various oxypropanolamine compounds, still remaining a phenyl aldehyde moiety, were then performed by Hantzsch condensation reaction with methylacetoacetate or ethylacetoacetate, respectively, to give our new series of dihydropyridine linked with the 4-phenyl ring. These compounds were evaluated for inotropic, chronotropic, and aorta contractility that associated with calcium channel and adrenoceptor antagonist activities. Dihydropyridine derivatives that with oxypropanolamine side chain on their 4-phenyl ring associated alpha-/beta-adrenoceptor blocking activities created a new family of calcium entry and the third generation beta-adrenoceptor blockers. Optimizing this research to obtain more potent alpha-/beta-adrenoceptor blocking and long-acting antihypertensive oxypropanolamine on the 4-phenyl ring of dihydropyridine series compounds was thus accomplished and classified as third generation dihydropyridine type calcium channel blockers, in comparison with previous short-acting type nifedipine and long-acting type amlodipine. We concluded that compounds 1a, 1b and 1g showed not only markedly high calcium-antagonistic activity but also the highest antihypertensive effect; compounds 1b, 1c, 1f, 1g, 1i and 1j induced sustained antihypertensive effects are major and attributed to their calcium entry and alpha-adrenoceptor blocking activities in the blood vessel due to their introduction of 2-methoxy, 1-oxyethylamino benzene moiety in the side chain on the 4-phenyl ring of dihydropyridine. Bradycardiac effects of all the compounds 1a-1j resulted from calcium entry and beta-adrenoceptor blocking, which attenuate the sympathetic activation-associated reflex tachycardia in the heart. We selected compound 1b as candidate compound for further pharmacological and pre-clinical evaluation studies.     

Tetrazole analogues of cyclolinopeptide A: synthesis, conformation, and biology

Linear and cyclic analogues of cyclolinopeptide A (CLA) with two dipeptide segments (Val(5)-Pro(6) and Pro(6)-Pro(7)) replaced by their tetrazole derivatives were synthesized by the SPPS technique and cyclized using TBTU (O-(benzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate) reagent. The conformational properties of the c(Leu(1)-Ile(2)-Ile(3)-Leu(4)-Val(5)-Pro(6)-psi[CN(4)]-Ala(7)-Phe(8)-Phe(9)) were investigated by NMR and computational techniques. The overall solution structure of this cyclic peptide resembles that observed for the CLA in the solid state. These studies of cyclic tetrazole CLA analogue confirm that the 1,5-disubstituted tetrazole ring functions as an effective, well-tolerated cis-amide bond mimic in solution. The peptides were examined for their immunosuppressive activity in the humoral response test. For cyclic analogues the immunosuppressive activity, at low doses, is equal in magnitude to the activity presented by cyclosporin A and native CLA. The conformational and biological data seem indicate that the Pro-Pro-Phe-Phe moiety and the preservation of the CLA backbone conformation are important for immunosuppressive activity.     

Biotin reagents in antibody pretargeting. 6. Synthesis and in vivo evaluation of astatinated and radioiodinated aryl- and nido-carboranyl-biotin derivatives

An investigation has been conducted to prepare and evaluate several radiohalogenated biotin derivatives as part of our studies to develop reagents for carrying (211)At in cancer pretargeting protocols. The primary goal of the investigation was to determine the in vivo stability and distribution properties of astatinated biotin derivatives. In addition to astatination, the biotin derivatives were radioiodinated for in vitro and in vivo comparison. Biodistributions were conducted in athymic mice, with sacrifice times of 1, 4, and 24 h to correspond to 9%, 32%, and 90% of (211)At decay (t(1/2) = 7.21 h). In the investigation, two biotin derivatives, 1a and 2a, were synthesized which had structures that contain a biotin moiety, a biotinidase-blocking moiety, an ether linker moiety, and an aryl stannane moiety for radiohalogenation. Biotin derivatives 1a and 2a were radiolabeled with (125/131)I to give [(125)/(131)I]1b or [(125)I]2b and with (211)At to give [(211)At]1c or [(211)At]2c. In vivo studies demonstrated that co-injected [(125)I]2b and [(131)I]1b had very similar tissue distributions in athymic mice. Co-injection of [(211)At]2c and [(125)I]2b provided data that indicated that rapid deastatination occurred in vivo. A second set of biotin derivatives, 3a, 4a, and 5a, were synthesized which had structures that contain a biotin moiety, a biotinidase-blocking moiety, and an anionic nido-carborane moiety for radiohalogenation. The biotin derivatives 4a and 5a contained an aryl moiety not present in 3a, and 5a had a trialkylamine functionality not present in 3a or 4a. Biotin derivative 3a was radioiodinated, but was not further investigated. Biotin derivatives 4a and 5a were radiolabeled with (211)At and (125)I to produce [(125)I]4b/[(211)At]4c and [(125)I]5b/[(211)At]5c. Comparison of [(125)I]4b and (separately) [(125)I]5b with [(131)I]1b showed that the nido-carborane containing biotin derivatives were retained in blood and tissue more than the aryl iodide derivative. In vivo evaluations of [(211)At]4c/[(125)I]4b and (separately) [(211)At]5c/[(125)I]5b indicated that some deastatination occurred in these compounds, but it was much less than observed for the aryl derivative [(211)At]2c. While the nido-carborane containing biotin derivatives provide a significant improvement in astatine stability over biotin derivatives previously studied, additional derivatives need to be prepared and studied to further improve the in vivo stability and blood/tissue clearance of these compounds.     

Caprolactams as potent CGRP receptor antagonists for the treatment of migraine

Calcitonin gene-related peptide (CGRP) has been implicated in the pathogenesis of migraine. Replacements for the benzodiazepine core of an earlier lead structure 1 including 5-, 6-, and 7-membered lactams were explored. Within the 7-membered ring scaffold, phenyl substitution at various positions afforded the potent (3R)-amino-(6S)-phenyl caprolactam template. The phenylimidazolinone privileged structure gave additional potency enhancements, as 24 showed good potency in both CGRP binding (K(i)=2 nM) and cAMP (IC(50)=4 nM) assays and was orally bioavailable in rats (27%).     

Axial chirality and affinity at the GABA(A) receptor of pyrimido[1,2-a][1,4]benzodiazepines and related compounds

The pyrimido[1,2-a][1,4]benzodiazepines (1a-c) and the 8-membered analogues (diazocines 2a and 2b) were separated into their atropisomers with HPLC on a chiral column. High stereochemical stability was observed in the atropisomer of the 8-membered derivatives (2a and 2b), and the 1,4-benzodiazepine (1c) with 2'-chloro at the pendant phenyl showed a lower energy barrier for the conversion between the atropisomers compared with that with the unsubstituted pendant phenyl (1a). The aR isomer of 1a-c was revealed to be the eutomer in GABA(A) receptor binding, and the eutomer 1c-R showed extremely potent activity with an IC(50) value of 1.5 nM.