The Palladium-Catalyzed Cross-Coupling Reaction of Phenylboronic Acid with Haloarenes in the Presence of Bases

Synthesis of Biaryls via a Nickel(0)-Catalyzed Cross-Coupling Reaction of Chloroarenes with Arylboronic Acids

The cross-coupling reaction of arylboronic acid with chloroarenes to give biaryls was carried out in high yields at 70-80 degrees C in the presence of a nickel(0) catalyst and K(3)PO(4) (3 equiv) in dioxane or benzene. The nickel(0) catalyst in situ prepared from NiCl(2).L (L = dppf, 2PPh(3)) (3-10 mol %) and 4 equiv of BuLi at room temperature was recognized to be most effective. The reaction can be applicable to a wide range of chloroarenes having an electron-withdrawing or an electron-donating group such as 4-NC, 4-CHO, 2- or 4-CO(2)Me, 4-COMe, 4-NHAc, 4-Me, 4-OMe, 4-NH(2), and 4-NMe(2). The Hammett's plot of the substituent effect of chloroarenes revealed that the reaction involves a rate-determining oxidative addition of chloroarenes to the nickel(0) complex.

Highly Efficient Palladium-Catalyzed Boronic Acid Coupling Reactions in Water: Scope and Limitations

The "ligandless" palladium acetate-catalyzed Suzuki cross-coupling reaction of ArX with aryl- and vinylboronic acids in water without organic cosolvent in the presence of tetrabutylammonium bromide is reported. Aryl bromides give high yields and considerably accelerate the coupling. A wide variety of functional groups can be tolerated. Aryl iodides, however, give incomplete conversion and aryl triflate coupling shows no improvement over reported conditions.

(2-Methyl-5-(methylsulfonyl)benzoyl)guanidine Na+/H+ antiporter inhibitors

The inhibition of the Na+/H+ exchanger during cardiac ischemia and reperfusion has been shown to be beneficial for the preservation of the cellular integrity and functional performance. The aim of the present investigation was to come up with potent and selective benzoylguanidines as NHE inhibitors for their use as an adjunctive therapy in the treatment of acute myocardial infarction. During the course of our investigations it became clear that the substitution ortho to the acylguanidine was of crucial importance for the potency of the compounds. 4-Chloro- and 4-fluoro-2-methylbenzoic acids 6 and 7 were prepared using the directed ortho metalation technique with the carboxylic acid as the directing group. With the LDA/methyl iodide system the 2-methyl group could be extended to an ethyl group. 4-Alkyl groups were inserted by the palladium-catalyzed cross-coupling reaction into the 4-bromo-2-methylbenzoic acid methyl ester (20). Starting with benzoic acids 6-19, the methylsulfonyl group was introduced by a sequence of standard reactions (sulfochlorination, reduction, and methylation). 4-Aryl derivatives 68-75 were synthesized by the palladium-catalyzed Suzuki reaction. A large number of nucleophilic displacement reactions in the 4-position were carried out with S-, O-, and N-nucleophiles as well as with the cyano and trifluoromethyl group. Using the ester method, acid chlorides, or Mukaiyama's procedure, the 5-(methylsulfonyl)benzoic acid derivatives were finally converted to the (5-(methylsulfonyl)benzoyl)guanidines 165-267 with excessive guanidine. In some cases nucleophilic substitutions with pyridinols and piperidine derivatives were carried out at the end of the reaction sequence with the 4-halo-N-(diaminomethylene)-5-(methylsulfonyl)-benzamides. Variations in the 4-position were most reasonable, but the volume of the substituents was of crucial importance. Substitution in the 3- and particularly in the 6-position led to considerable worsening of the inhibitory effects of the Na+/H+ exchanger. The 2-methyl compounds, however, showed without exception higher in vitro activities than their respective demethyl counterparts as they are exemplified by the reference compounds 266 and 267, obviously caused by a conformational restriction of the acylguanidine chain. The development compound (2-methyl-5-(methylsulfonyl)-4-pyrrolobenzoyl)guanidine, methanesulfonate (246) is a NHE-1 subtype specific NHE inhibitor, being 27-fold more potent toward the NHE-1 than the NHE-2 isoform. 246 was found to act cardioprotectively not only when given before an experimentally induced ischemia, but also curatively after the onset of symptoms of acute myocardial infarction when given prior to the induction of reperfusion.

Substituted hexahydrobenzo[f]thieno[c]quinolines as dopamine D1-selective agonists: synthesis and biological evaluation in vitro and in vivo

A series of substituted 9,10-dihydroxyhexahydrobenzo[f]thieno[c]quinolines (TB[f]Q), varying with respect to the position of the thiophene relative to the benzo[f]quinoline core and the nature and position of the substituent on the thiophene, were prepared and evaluated for their affinity and selectivity for the dopamine D1-like receptor. The thieno[3,2-c]B[f]Q regioisomers bearing a small alky1 (C1-C3) substituent at the 2 position were potent (Ki < 20 nM) and selective (D2/D1 > 50) D1 agonists with close to full agonist activity (IA > 85%). The compounds were resolved and found to exhibit a high level of enantiospecificity in their interaction with the D1 receptor. Selected compounds were tested in vivo in the 6-OHDA rodent model of Parkinson's disease and for their liability to produce seizure-like activities in mice. (5aR)-trans-2-Propyl-4,5,5a,6,7, 11b-hexahydro-3-thia-5-azacyclopent-1-ena[c]phenanthrene-9,10-diol (5) emerged as the compound with the best overall in vivo profile in terms of potency (ED50 = 0.04 mumol/kg) and safety.

Synthetic Applications of 3,4-Bis(trimethylsilyl)thiophene: Unsymmetrically 3,4-Disubstituted Thiophenes and 3,4-Didehydrothiophene(,)

3,4-Bis(trimethylsilyl)thiophene (1a) was synthesized by three routes: (a) 1,3-dipolar cycloaddition; (b) modification of 3,4-dibromothiophene; and (c) intermolecular thiazole-alkyne Diels-Alder reaction. 3,4-Bis(trimethylsilyl)thiophene (1a) can function as a versatile building block for the construction of unsymmetrically 3,4-disubstituted thiophenes utilizing its stepwise regiospecific mono-ipso-substitution followed by palladium-catalyzed cross-coupling reactions. In this manner, thiophenes 15, 16, 17a-j, 19a,b, 20, 22a-c, 23a,b, 24a-d, 25a-c, and 27a-j were prepared. The thiophene-3,4-diyl dimer 28 and thiophene-3,4-diyl tetramer 29 were also realized by palladium-catalyzed self-coupling reaction of organoboroxines. The stannylthiophene 31, formed by conversion of the C-Si bond to a C-Sn bond via boroxine 26c underwent both carbonylative coupling and lithiation followed by quenching with electrophiles to afford unsymmetrically 3,4-disubstituted thiophenes 33 and 36a-c as well. Moreover, 3,4-bis(trimethylsilyl)thiophene (1a) can be used as the starting material for the generation of the highly strained cyclic cumulene 3,4-didehydrothiophene (2), whose existence was substantiated by its trapping reaction with several alkenes.

Inhibition of stromelysin-1 (MMP-3) by P1'-biphenylylethyl carboxyalkyl dipeptides

Carboxyalkyl peptides containing a biphenylylethyl group at the P1' position were found to be potent inhibitors of stromelysin-1 (MMP-3) and gelatinase A (MMP-2), in the range of 10-50 nM, but poor inhibitors of collagenase (MMP-1). Combination of a biphenylylethyl moiety at P1', a tert-butyl group at P2', and a methyl group at P3' produced orally bioavailable inhibitors as measured by an in vivo model of MMP-3 degradation of radiolabeled transferrin in the mouse pleural cavity. The X-ray structure of a complex of a P1-biphenyl inhibitor and the catalytic domain of MMP-3 is described. Inhibitors that contained halogenated biphenylylethyl residues at P1' proved to be superior in terms of enzyme potency and oral activity with 2(R)-[2-(4'-fluoro-4-biphenylyl)ethyl]-4(S)-n-butyl-1,5-pentane dioic acid 1-(alpha(S)-tert-butylglycine methylamide) amide (L-758,354, 26) having a Ki of 10 nM against MMP-3 and an ED50 of 11 mg/kg po in the mouse pleural cavity assay. This compound was evaluated in acute (MMP-3 and IL-1 beta injection in the rabbit) and chronic (rat adjuvant-induced arthritis and mouse collagen-induced arthritis) models of cartilage destruction but showed activity only in the MMP-3 injection model (ED50 = 6 mg/kg iv).

Synthesis, antimalarial activity, and molecular modeling of tebuquine analogues

Tebuquine (5) is a 4-aminoquinoline that is significantly more active than amodiaquine (2) and chloroquine (1) both in vitro and in vivo. We have developed a novel more efficient synthetic route to tebuquine analogues which involves the use of a palladium-catalyzed Suzuki reaction to introduce the 4-chlorophenyl moiety into the 4-hydroxyaniline side chain. Using similar methodology, novel synthetic routes to fluorinated (7a, b) and a dehydroxylated (7c) analogue of tebuquine have also been developed. The novel analogues were subjected to testing against the chloroquine sensitive HB3 strain and the chloroquine resistant K1 strain of Plasmodium falciparum. Tebuquine was the most active compound tested against both strains of Plasmodia. Replacement of the 4-hydroxy function with either fluorine or hydrogen led to a decrease in antimalarial activity. Molecular modeling of the tebuquine analogues alongside amodiaquine and chloroquine reveals that the inter-nitrogen separation in this class of drugs ranges between 9.36 and 9.86 A in their isolated diprotonated form and between 7.52 and 10.21 A in the heme-drug complex. Further modeling studies on the interaction of 4-aminoquinolines with the proposed cellular receptor heme revealed favorable interaction energies for chloroquine, amodiaquine, and tebuquine analogues. Tebuquine, the most potent antimalarial in the series, had the most favorable interaction energy calculated in both the in vacuo and solvent-based simulation studies. Although fluorotebuquine (7a) had a similar interaction energy to tebuquine, this compound had significantly reduced potency when compared with (5). This disparity is possibly the result of the reduced cellular accumulation (CAR) of fluorotebuquine when compared with tebuquine within the parasite. Measurement of the cellular accumulation of the tebuquine analogues and seven related 4-aminoquinolines shows a significant relationship (r = 0.98) between the CAR of 4-aminoquinoline drugs and the reciprocal of drugs IC50.

Synthesis and structure-activity relationship of a new series of potent AT1 selective angiotensin II receptor antagonists: 5-(biphenyl-4-ylmethyl)pyrazoles

The synthesis and pharmacological activity of a new series of 5-(biphenyl-4-ylmethyl)pyrazoles as potent angiotensin II antagonists both in vitro (binding of [3H]AII) and in vivo (iv, inhibition of AII-induced increase in blood pressure, pithed rats; po, furosemide-treated sodium-depleted rats) are reported. The various substituents of the pyrazole ring have been modified taking into account the receptor's requirements derived from related structure-activity relationship studies. A propyl or butyl group at position 1 as well as a carboxylic acid group at position 4 were shown to be essential for high affinity. Different groups at position 3 (H, small alkyl, phenyl, benzyl) provided good binding affinity, but oral activity was highly discriminating: bulky alkyl groups provided the highest potencies. Among the acidic isosteres tested in the biphenyl moiety, the tetrazole group proved to be the best. Compound 14n (3-tert-butyl-1-propyl-5-[[2'-(1H-tetrazol-5-yl)-1,1'-biphenyl-4-y l] methyl]-1H-pyrazole-4-carboxylic acid, UR-7280) shows high potency both in vitro (IC50 = 3 nM) and in vivo (iv, 61.2 +/- 10% decrease in blood pressure at 0.3 mg/kg; po, 30 mmHg fall in blood pressure at 0.3 mg/kg), in comparison to losartan (IC50 = 59 nM; iv, 62.5 +/- 8.9% decrease in blood pressure at 1 mg/kg; po, 13 mmHg fall in blood pressure at 3 mg/kg). These data, together with the good pharmacokinetic profile of 14n in different species, have led to its selection for clinical evaluation as an antihypertensive agent.