Synthesis and Biological Activity of C-Acyclic Nucleosides of Imidazo [1,5-a]-1,3,5-Triazines

Abstract

C-acyclic nucleoside analogues of inosine and guanosine 8-[(RS)-2,3-dihydroxypropyl] imidazo [1,5-a]-1,3,5-triazin-4 (3H)-ones 6a, c, d were synthesized. The route involved the cyclization-rearrangement of 5-acylamino-5-allyl-6-amino-4,5-dihydropyrimidin-4-ones 4a-c to 8-allylimidazo [1,5-a]-1,3,5-triazin-4 (3H) ones 5a-c. 5a was transformed selectively into 5d by reductive desulfurization with highly deactivated Raney nickel. The poorly soluble compounds 5b and 5c were converted to N-2-acetylated 5f and 5g. Osmium tetroxide hydroxylation of 5d, f, g gave 6a, c, d. None of the newly synthesized C-acyclic nucleoside derivatives showed an appreciable antiviral or antitumor cell activity.     

Mefloquine-oxazolidine derivatives, derived from mefloquine and arenecarbaldehydes: In vitro activity including against the multidrug-resistant tuberculosis strain T113

Ten new mefloquine-oxazolidine derivatives, 4-[(1S,8aR)-3-(aryl)hexahydro[1,3]oxazolo[3,4-a]pyridin-1-yl]-2,8-bis(trifluoromethyl)quinoline (1: aryl=substituted phenyl) and 4-[(1S,8aR)-3-(heteroaryl)hexahydro[1,3]oxazolo[3,4-a]pyridin-1-yl]-2,8-bis(trifluoromethyl)quinoline [2: heteroaryl=5-nitrothien-2-yl (2a); 5-nitrofuran-2-yl (2b) and 4H-imidazol-2-yl) (2c)], have been synthesized and evaluated against Mycobacterium tuberculosis. Compounds 1f (aryl=3-ethoxyphenyl), 1g (Ar=3,4,5-(MeO)(3)-C(6)H(2)) and 2c were slightly more active than mefloquine (MIC=33μM) with MICs=24.5, 22.5 and 27.4, respectively, whereas compounds 1e (aryl=3,4-(MeO)(2)-C(6)H(3)) and 2a (MICs=11.9 and 12.1μM, respectively) were ca. 2.7 times more active than mefloquine, with a better tuberculostatic activity than the first line tuberculostatic agent ethambutol (MIC=15.9). The compounds were also assayed against the MDR strain T113 and the same MICs were observed. Thus the new derivatives have advantages over such anti-TB drugs as isoniazid, rifampicin, ethambutol and ofloxacin, for which this strain is resistant. The most active compounds were not cytotoxic to Murine Macrophages Cells in a concentration near their MIC values.     

Synthesis of s-triazine-based thiazolidinones as antimicrobial agents

A novel series of thiazolidinone derivatives, namely 4-{4-dimethylamino-6-[4-oxo-2-phenyl-5-(4-pyridin-2-yl-piperazin-1-ylmethyl)-thiazolidin-3-yl]-[1,3,5]-triazin-2-yloxy}-1-methyl-1H-quinolin-2-ones, have been synthesized from the key intermediate 4-(4-amino-6-dimethylamino-[1,3,5]-triazin-2-yloxy)-1-methyl-1H-quinolin-2-one (5). Compound 5 was condensed with various aldehydes to give Schiff base derivatives, which after cyclization gave thiazolidinones that were linked with 1-pyridin-2-yl-piperazine to obtain the target compounds. The newly synthesized compounds were evaluated for their antimicrobial activity against eight bacteria (Staphylococcus aureus, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Salmonella typhi, Proteus vulgaris, Shigella flexneri) and four fungi (Aspergillus niger, Candida albicans, Aspergillus fumigatus, Aspergillus clavatus).     

Phosphodiesterase inhibitors. Part 4: Design, synthesis and structure-activity relationships of dual PDE3/4-inhibitory fused bicyclic heteroaromatic-4,4-dimethylpyrazolones

(-)-6-(7-Methoxy-2-trifluoromethylpyrazolo[1,5-a]pyridin-4-yl)-5-methyl-4,5-dihydro-3-(2H)-pyridazinone (KCA-1490) is a dual PDE3/4 inhibitor that exhibits potent combined bronchodilatory and anti-inflammatory activity. Here we show that a 4,4-dimethylpyrazolone subunit serves as an effective surrogate for the 5-methyl-4,5-dihydropyridazin-3(2H)-one ring of KCA-1490 whilst lacking a stereogenic centre. The 2- and 7-substituents in the pyrazolo[1,5-a]pyridine subunit markedly influence the PDE-inhibitory profile and can be adjusted to afford either potent PDE4-selective inhibitors or dual PDE3/4 inhibitors. A survey of bicyclic heteroaromatic replacements for the pyrazolo[1,5-a]pyridine allowed further refinement of the inhibitory profile and identified 3-(8-methoxy-2-(trifluoromethyl)imidazo[1,2-a]pyridin-5-yl)-4,4-dimethyl-1H-pyrazol-5(4H)-one as an orally active, achiral KCA-1490 analog with well-balanced dual PDE3/4-inhibitory activity.     

Phosphodiesterase inhibitors. Part 3: Design, synthesis and structure-activity relationships of dual PDE3/4-inhibitory fused bicyclic heteroaromatic-dihydropyridazinones with anti-inflammatory and bronchodilatory activity

(-)-6-(7-Methoxy-2-trifluoromethylpyrazolo[1,5-a]pyridin-4-yl)-5-methyl-4,5-dihydro-3-(2H)-pyridazinone (KCA-1490) is a dual PDE3/4 inhibitor that exhibits potent combined bronchodilatory and anti-inflammatory activity. A survey of potential bicyclic heteroaromatic replacement subunits for the pyrazolo[1,5-a]pyridine core of KCA-1490 has identified the 4-methoxy-2-(trifluoromethyl)benzo[d]thiazol-7-yl and 8-methoxy-2-(trifluoromethyl)quinolin-5-yl analogues as dual PDE3/4-inhibitory compounds that potently suppress histamine-induced bronchoconstriction and exhibit anti-inflammatory activity in vivo.     

Synthesis and biological evaluation of 1-substituted-3-(6-methylpyridin-2-yl)-4-([1,2,4]triazolo[1,5-a]pyridin-6-yl)pyrazoles as transforming growth factor-β type 1 receptor kinase inhibitors

A series of 1-substituted-3-(6-methylpyridin-2-yl)-4-([1,2,4]triazolo[1,5-a]pyridin-6-yl)pyrazoles 14a-ae, 16a, 16b, and 21a-c has been prepared and evaluated for their ALK5 inhibitory activity in an enzyme assay and in a cell-based luciferase reporter assay. The 4-([1,2,4]triazolo[1,5-a]pyridin-6-yl)-N-(4-methoxyphenyl)-3-(6-methylpyridin-2-yl)-1H-pyrazole-1-carbothioamide (14n) inhibited ALK5 phosphorylation with IC(50) value of 0.57 nM and showed 94% inhibition at 100 nM in a luciferase reporter assay using HaCaT cells permanently transfected with p3TP-luc reporter construct.     

Discovery and pharmacological characterization of N-[2-({2-[(2S)-2-cyanopyrrolidin-1-yl]-2-oxoethyl}amino)-2-methylpropyl]-2-methylpyrazolo[1,5-a]pyrimidine-6-carboxamide hydrochloride (anagliptin hydrochloride salt) as a potent and selective DPP-IV inhibitor

In the course of our program for discovery of novel DPP-IV inhibitors, a series of pyrazolo[1,5-a]pyrimidines were found to be novel DPP-IV inhibitors. We identified N-[2-({2-[(2S)-2-cyanopyrrolidin-1-yl]-2-oxoethyl}amino)-2-methylpropyl]-2-methylpyrazolo[1,5-a]pyrimidine-6-carboxamide hydrochloride (4a) and described its pharmacological profiles.     

Comparison of different heterocyclic scaffolds as substrate analog PDE5 inhibitors

Several different heterocyclic systems were compared as PDE5 inhibitor scaffolds. In addition to the known 3H-imidazo[5,1-f][1,2,4]triazin-4-ones and pyrazolopyrimidinones, isomeric imidazo[1,5-a][1,3,5]triazin-4(3H)-ones were also shown to be potent and selective PDE inhibitor scaffolds with in vivo activity. SAR trends were elucidated for sulfonamide derivatives with generality across different scaffolds.     

Novel selective antagonist radioligands for the pharmacological study of A2B adenosine receptors

The adenosine A_2B receptor is the least well characterized of the four adenosine subtypes due to the lack of potent and selective agonists and antagonists. Despite the widespread distribution of A_2B receptor mRNA, little information is available with regard to their function. The characterization of A_2B receptors, through radioligand binding studies, has been performed, until now, by using low-affinity and non-selective antagonists like 1,3-dipropyl-8-cyclopentylxanthine ([³H]DPCPX),(4-(2-[7-amino-2-(2-furyl)-[1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-ylamino]ethyl)-phenol ([³H]ZM 241385) and 3-(3,4-aminobenzyl)-8-(4-oxyacetate)phenyl-1-propyl-xanthine ([¹²⁵I]ABOPX). Recently, high-affinity radioligands for A_2B receptors, [N-(4-cyanophenyl)-2-[4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)-phenoxy]acetamide ([³H]MRS 1754), N-(2-(2-Phenyl-6-[4-(2,2,3,3-tetratritrio-3-phenylpropyl)-piperazine-1-carbonyl]-7H-pyrrolo[2,3-d]pyrimidin-4-ylamino)-ethyl)-acetamide ([³H]OSIP339391) and N-benzo[1,3]dioxol-5-yl-2-[5-(1,3-dipropyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yloxy]-acetamide] ([³H]MRE 2029F20), have been introduced. This minireview offers an overview of these recently developed radioligands and the most important applications of drugs towards A_2B receptors.     

Syntheses of phenylpyrazolodiazepin-7-ones as conformationally rigid analogs of aminopyrazole amide scaffold and their antiproliferative effects on cancer cells

Recently, we have reported the syntheses and antiproliferative activities of N-(5-amino-1-(4-methoxybenzyl)-1H-pyrazol-4-yl amide derivatives on melanoma cells. As a continuous work for antiproliferative agents in melanoma, here we report the synthesis of conformationally rigid analogs, phenyl-6,8-dihydropyrazolo[3,4-b][1,4]diazepin-7(1H)-one derivatives 7a-g, 8a-o and their antiproliferative activities against A375P melanoma cell line and U937 hematopoietic cell line. Most compounds showed competitive antiproliferative activities to sorafenib, the reference standard. Among them, N-(3-(1-benzyl-7-oxo-1,6,7,8-tetrahydropyrazolo[3,4-b][1,4]diazepin-5-yl)phenyl)-4-chloro-3-(trifluoro methyl)benzamide-amino-1-(4-methoxybenzyl)-1H-pyrazol-4-yl)-5-(3-(4-chloro-3-(trifluoromethyl) phenyl) ureido)-2-methylbenzamide (7b) exhibited potent activities (GI(50)=0.43 μM and 0.06 μM) on both cell lines. It has been further confirmed to be a potent and selective Raf kinases inhibitor and also mild inhibitor of PI3Kα.     

Synthesis of some novel pyrazolo[3,4-d]pyrimidine derivatives as potential antimicrobial agents

The reaction of 4-hydrazino-8-(trifluoromethyl)quinoline (2) with ethoxymethylenecyanoacetate afforded ethyl 5-amino-1-[8-(trifluoromethyl)quinolin-4-yl]-1H-pyrazole-4-carboxylate (3) and that with ethoxymethylenemalononitrile afforded 5-amino-1-[8-(trifluoromethyl)quinolin-4-yl]-1H-pyrazole-4-carbonitrile (5). Compounds 3 and 5 were hydrolyzed to get 5-amino-1-[8-(trifluoromethyl)quinolin-4-yl]-1H-pyrazole-4-carboxylic acid and then reacted with acetic anhydride to afford 6-methyl-1-[8-(trifluoromethyl)quinolin-4-yl]pyrazolo[3,4-d]oxazin-4-one (6), which was condensed with different aromatic amines to give a series of 5-substituted 6-methyl-1-[8-(trifluoromethyl)quinolin-4-yl]-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-ones (7). Compounds 3 and 5 also reacted with formamide, urea, and thiourea affording the corresponding pyrazolo[3,4-d]pyrimidines (8-13), respectively. Structures of the products have been determined by chemical reactions and spectral studies. All compounds of the series have been screened for their antibacterial and antifungal activity studies. The results are summarized in Tables 1 and 2.     

3H]Ro 15-1788 binding sites to brain membrane of the saltwater Mugil cephalus

The equilibrium binding parameters of the benzodiazepine antagonist [3H]Ro 15-1788 (8-fluoro-3-carboethoxy-5,6-dihydro-5-methyl-6-oxo-4H-imidazol-[1,5-a]-1,4 benzodiazepine) were evaluated in brain membranes of the saltwater teleost fish, Mugil cephalus. To test receptor subtype specificity, displacement studies were carried out by competitive binding of [3H]Ro 15-1788 against six benzodiazepine receptor ligands, flunitrazepam [5-(2-fluoro-phenyl)-1,3-dihydro-1-methyl-7-nitro-2H-1,4-benzodiazepin-2-one], alpidem [N,N-dipropyl-6-chloro-2-(4-chlorophenyl)imidazo[1,2-a]pyridine-3-acetamide], zolpidem [N,N-6 trimethyl-2-(4-methyl-phenyl)imidazo[1,2-a]pyridine-3-acetamide hemitartrate], and beta-CCM (methyl beta-carboline-3-carboxylate). Saturation studies showed that [3H]Ro 15-1788 bound saturatably, reversibly and with a high affinity to a single class of binding sites (Kd value of 1.18-1.5 nM and Bmax values of 124-1671 fmol/mg of protein, depending on brain regions). The highest concentration of benzodiazepine recognition sites labeled with [3H]Ro 15-1788 was present in the optic lobe and the olfactory bulb and the lowest concentration was found in the medulla oblongata, cerebellum and spinal cord. The rank order of displacement efficacy of unlabelled ligands observed suggested that central-type benzodiazepine receptors are present in one class of binding sites (Type I-like) in brain membranes of Mugil cephalus. Moreover, the uptake of 36Cl- into M. cephalus brain membrane vesicles was only marginally stimulated by concentrations of GABA that significantly enhanced the 36Cl- uptake into mammalian brain membrane vesicles. The results may indicate a different functional activity of the GABA-coupled chloride ionophore in the fish brain as compared with the mammalian brain.     

Synthesis and SAR of 3-arylsulfonyl-pyrazolo[1,5-a]pyrimidines as potent serotonin 5-HT6 receptor antagonists

Syntheses of a series of novel 3-sulfonyl-pyrazolo[1,5-a]pyrimidines and their 5-HT(6) receptor antagonistic structure-activity relationship are disclosed. The nature and position of substituents, which affect their receptor antagonistic activity, are analyzed. Among all synthesized derivatives, {3-(3-chlorophenylsulfonyl)-5,7-dimethyl-pyrazolo[1,5-a]pyrimidin-2-yl}-methyl-amine 33 (K(i)=190 pM), (3-phenylsulfonyl-7-methyl-pyrazolo[1,5-a]pyrimidin-2-yl)-methyl-amine 44 (K(i)=240 pM), (3-phenylsulfonyl-5-metoxymethyl-7-methyl-pyrazolo[1,5-a]pyrimidin-2-yl)-methyl-amine 50 (K(i)=270 pM), and (3-phenylsulfonyl-5-methyl-7-metoxymethyl-pyrazolo[1,5-a]pyrimidin-2-yl)-methyl-amine 52 (K(i)=280 pM) are the most potent antagonists of the 5-HT(6) receptors.     

Short and Straightforward Synthesis of Triphosphates of Artificial Nucleobase Pairs Displaying Unconventional Pairing Scheme

Concise, facile and efficient synthesis of 5′-O-triphosphates of 6-amino-5-nitro-3-(1′-β-D-2′-deoxyribofuranosyl)-2(1H)-pyridone (dZ) and its Watson-Crick complement 2-amino-8-(1′-β-D-2′-deoxyribofuranosyl)-imidazo[1,2a]-1,3,5-triazin-4(8H)-one (dP) is reported using a one-pot synthetic procedure.     

Synthesis and analgesic/anti-inflammatory evaluation of fused heterocyclic ring systems incorporating phenylsulfonyl moiety

A series of pyrazolo[1,5-a]pyrimidine, triazolo[1,5-a]pyrimidine, and pyrimido[1,2-a]benzimidazole ring systems incorporating phenylsulfonyl moiety were synthesized via the reaction of 3-(N,N-dimethylamino)-1-aryl-2-(phenylsulfonyl)prop-2-en-1-one derivatives 2a,b with appropriate nitrogen nucleophiles. The analgesic and anti-inflammatory activities of the newly synthesized compound were investigated in vivo. 3-Bromo-2-phenyl-6-(phenylsulfonyl)-7-(4-methylphenyl)pyrazolo[1,5-a]pyrimidine (5e) was found to have an excellent analgesic activity in comparison with indomethacin as a reference drug, while the highest anti-inflammatory effect was observed in the case of 2-(4-bromophenyl)-6-(phenylsulfonyl)-5-(4-methylphenyl)pyrazolo[1,5-a]pyrimidine (5d). From the structure-activity relationship (SAR) point of view, the analgesic/anti-inflammatory activity of pyrazolo[1,5-a]pyrimidine derivatives was found to be much higher than triazolo[1,5-a]pyrimidine and pyrimido[1,2-a]benzimidazole derivatives.     

Ring-Opening of 3-β-D-Ribofuranosyl-3,7,8,9-Tetrahydropyrimido [1,2-i]Purin-8-ol and Preparation of 2-Thio- and 2-aza-Adenosine Derivatives

The adduct 3-β-D-ribofuranosyl-3,7,8,9-tetrahydropyrimido[1,2-i]purin-8-ol (2), obtained from adenosine and epichlorohydrin, underwent ring fission at basic conditions. The initial ring-opening took place at C2 of the pyrimidine unit resulting in 2-(5-amino-1-β-D-ribofuranosyl-imidazol-4-yl)-1,4,5,6-tetrahydropyrimidin-5-ol (3). Also the tetrahydropyrimidine ring of 3 could be opened resulting in 5-amino-1-(β-D-ribofuranosyl)-imidazole-4-(N-3-amino-2-hydroxyl-propyl)-carboxamide (4). In hot acid conditions, 2 was both deglycosylated and ring-opened yielding 2-(5-amino-imidazol-4-yl)-1,4,5,6-tetrahydropyrimidin-5-ol (7) as the final product. When reacting 3 with CS₂ or HNO₂ ring-closure took place and 3-β-D-ribofuranosyl-3,4,7,8,9-pentahydropyrimido[1,2-i]purin-8-ol-5-thione (5), and 3-β-D-ribofuranosyl-imidazo[4,5-e]-3,7,8,9-tetrahydropyrimido[1,2-c][1,2,3]triazine-8-ol (6), respectively, were obtained. Also, the pyrimidine ring of the epichlorohydrin adduct with adenine, 10-imino-5,6-dihydro-4H,10H-pyrimido[1,2,3-cd]purin-5-ol (10), underwent ring fission and the product was identified as 3-hydroxy-1,2,3,4-tetrahydroimidazo[1,5-a]pyrimidine-8-carboximidamide (11).     

Practical stereoselective synthesis of (2,3,4, 5-tetrahydro-1H-benzo[b]azepin-5-yl)acetic acid

Highly enantioselective asymmetric hydrogenation of readily accessible olefins, (E)- and (Z)-[1-(toluene-4-sulfonyl)-1,2,3, 4-tetrahydro-1H-benzo[b]azepin-5-ylidene]acetic acid (4a and 4b, respectively) and [1-(toluene-4-sulfonyl)-2, 3-dihydro-1H-benzo[b]azepin-5-yl]acetic acid (4c), is presented as an efficient and straightforward route to (R)-[1-(toluene-4-sulfonyl)-2,3,4, 5-tetrahydro-1H-benzo[b]azepin-5-yl]acetic acid [(R)-1] which is a key intermediate for the synthesis of non-peptide AVP V2-agonist. Hydrogenation of carboxylic acid 4c gave (R)-1 in quantitative yield and 85% ee using Ru(OAc)2[(S)-H8-BINAP], a Ru(II) complex of a partially hydrogenated BINAP (H8-BINAP), as a catalyst. When (R)-1 of 76% ee was transformed into the corresponding isopropylamide 6, pure enantiomer (R)-6 was obtained in 75% yield by recrystallization from MeOH.     

Novel vasopressin V2 receptor-selective antagonists, pyrrolo[2,1-a]quinoxaline and pyrrolo[2,1-c][1,4]benzodiazepine derivatives.

The intent of the work was to study the structure-activity relationships of AVP receptor antagonists bearing a chiral ring as a partial structure since such studies had been reported for only achiral compounds. In the present paper, we deal with compounds consisting of the chiral tricyclic hetero ring (1,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinoxaline and 1,2,3,10,11,11a-hexahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine) and 2-phenylbenzanilide analogues. These compounds exhibited a highly selective affinity for V2 receptor, and their stereochemical configuration had a great influence on V2 receptor binding. VP-343 (N-[4-[[(2S,3aR)-2-hydroxy-2,3,3a,4-tetrahydropyrrolo[1,2-a] quinoxalin-5(1H)-yl]carbonyl]phenyl]-4'-methyl[1,1'-biphenyl]-2-ca rboxamide), VP-365 (N-[4-[[(11aS)-2,3,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benz odiazepin-10(5H)-yl]carbonyl]phenyl][1,1'-biphenyl-2-carboxamide) and VP-339 (N-[4-[[(11aS)-5-oxo-2,3,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]+ ++benzodiazepin-10(5H)-yl]carbonyl]phenyl][1,1'-biphenyl]-2-carboxami de) were the most potent compounds in vitro and in vivo. The IC50 values of VP-343, VP-365 and VP-339 against V2 receptor were 0.772, 1.18 and 0.216 nM, respectively. The ED300 values (dose required to increase three times the urine volume of the control rats; oral administration) of VP-343, VP-365 and VP-339 were 0.22, 0.31 and 0.78 mg/kg, respectively.     

Synthesis and positive inotropic evaluation of N-(1-oxo-1,2,4,5-tetrahydro-[1,2,4]triazolo[4,3-a]quinolin-7-yl)acetamides bearing piperazine and 1,4-diazepane moieties

Two series of N-(1-oxo-1,2,4,5-tetrahydro-[1,2,4]triazolo[4,3-a]quinolin-7-yl)acetamides bearing piperazine and 1,4-diazepane moieties were synthesized and screened for their positive inotropic activity by measuring left atrium stroke volume on isolated rabbit heart preparations. Most of the derivatives exhibited better in vitro positive inotropic activity than the existing drug, milrinone, among which 2-(4-(4-chlorobenzyl)-1,4-diazepan-1-yl)-N-(1-oxo-1,2,4,5-tetrahydro-[1,2,4]triazolo[4,3-a]quinolin-7-yl)acetamide 6c proved to be the most potent with 15.48 ± 0.27% increased stroke volume (milrinone: 2.46 ± 0.07%) at a concentration of 3 × 10(-5) M. The chronotropic effects of the compounds that exhibited inotropic effects were also evaluated.     

Synthesis and positive inotropic activity of N-(4,5-dihydro-[1,2,4]triazolo[4,3-a]quinolin-7-yl)-2-(piperazin-1-yl)acetamide derivatives

A series of N-(4,5-dihydro-[1,2,4]triazolo[4,3-a]quinolin-7-yl)-2-(piperazin-1-yl)acetamide derivatives were synthesized and their positive inotropic activity was evaluated by measuring left atrium stroke volume on isolated rabbit heart preparations. Several compounds showed favorable activity compared with the standard drug, milrinone, among which N-(1-benzyl-4,5-dihydro-[1,2,4]triazolo[4,3-a]quinolin-7-yl)-2-(4-benzylpiperazin-1-yl)acetamide 6j was found to be the most potent with the 13.2% increased stroke volume (milrinone 4.7%) at concentration of 3x10(-5) M in our in vitro study. The chronotropic effects of those compounds having inotropic effects were also evaluated in this work.