Synthesis of 2-phenyl-5,6,7,8-tetrahydroquinoxaline derivatives and screening for P2X1-purinoceptor antagonist activity in isolated preparations of rat vas deferens, for translation into a male contraceptive†.

Sympathetically mediated contractions of smooth muscle cells in the vasa deferentia are mediated by neuronally released adenosine 5'-triphosphate (ATP) and noradrenaline, which stimulate P2X1-purinoceptors and α1A-adrenoceptors, respectively. This process is crucial for sperm transport, as demonstrated in knockout mouse studies where simultaneous genetic deletion of P2X1-purinoceptors and α1A-adrenoceptors resulted in male infertility. We hypothesize that dual pharmacological antagonism of these two receptors could inhibit sperm transport sufficiently to provide a novel nonhormonal method of male contraception. To generate a suitable P2X1-purinoceptor antagonist, substituents were introduced on the phenyl moiety of 2-phenyl-5,6,7,8-tetrahydroquinoxaline to create a series of analogues that were tested for P2X1-purinoceptor antagonism in isolated preparations of rat vas deferens. Novel compounds were initially screened for their ability to attenuate contractile responses to electrical field stimulation (EFS: 60 V, 0.5 ms, 0.2 Hz). The addition of polar substituents to the meta, but not ortho, position markedly increased the inhibition of contractions, as did the addition of both polar and aliphatic substituents to the para position. Di-substituted compounds were also synthesized and tested, resulting in a compound 31 (2-hydroxy, 4-fluoro), which exhibited the greatest potency, with an IC50 of 14 µM (95% confidence limits: 12-16 µM). Additionally, compound 31 noncompetitively antagonized contractions mediated by exogenously administered αß-methylene ATP (10 nM-30 µM) but had no inhibitory effect on contractions mediated by exogenously administered noradrenaline (30 nM-100 µM) or acetylcholine (30 nM-100 µM). These results have contributed to a structure-activity relationship profile for the P2X1-purinoceptor that will inform future designs of more potent antagonists.

Gold-Catalyzed Double Cycloisomerization of 1-Ene-4,10-diynyl Esters to Bicyclo[6.3.0]undeca-2,4,9-trienyl Esters.

A synthetic method to prepare bicyclo[6.3.0]undeca-2,4,9,trienyl esters efficiently from gold(I)-catalyzed Rautenstrauch rearrangement/1,5-hydride shift/8-endo-dig cyclization of 1-ene-4,10-diynyl esters is described. The suggested double cycloisomerization mechanism delineates the first example of an unactivated all-carbon tethered 1,7-enyne, either preformed or formed in situ, which undergoes an 8-endo-dig cyclization pathway to give a cyclooctane motif. It also offers an extremely rare synthetic method in organic chemistry that can sequentially assemble both ring components of the bicyclic motif from an acyclic precursor in one step.

Synthesis of 1,4-amino alcohols by Grignard reagent addition to THF and N-tosyliminobenzyliodinane.

The synthesis of 1,4-amino alcohols from THF treated with N-tosyliminobenzyliodinane (PhINTs) followed by a Grignard reagent under mild reaction conditions at room temperature is described herein. Various Grignard reagents were shown to be compatible, furnishing the corresponding 4-substituted-N-1,4-tosylamino alcohols in good to excellent yields. A partial or full detosylation of the N-tosyl-1,4-amino alcohol was observed in instances involving a sterically bulky Grignard reagent, leading to the deprotected 1,4-amino alcohol product in moderate to good yields. The synthetic utility of this protocol was demonstrated by the synthesis of a 5-substituted-N-tosyl-1,5-amino alcohol from THP and the conversion of two examples to their corresponding γ-lactam and pyrrolidine adducts.

Discovery of Potent and Fast-Acting Antimalarial Bis-1,2,4-triazines.

Novel 3,3'-disubstituted-5,5'-bi(1,2,4-triazine) compounds with potent in vitro activity against Plasmodium falciparum parasites were recently discovered. To improve the pharmacokinetic properties of the triazine derivatives, a new structure-activity relationship (SAR) investigation was initiated with a focus on enhancing the metabolic stability of lead compounds. These efforts led to the identification of second-generation highly potent antimalarial bis-triazines, exemplified by triazine 23, which exhibited significantly improved in vitro metabolic stability (8 and 42 µL/min/mg protein in human and mouse liver microsomes). The disubstituted triazine dimer 23 was also observed to suppress parasitemia in the Peters 4-day test with a mean ED50 value of 1.85 mg/kg/day and exhibited a fast-killing profile, revealing a new class of orally available antimalarial compounds of considerable interest.

Brønsted Acid-Mediated Cycloaromatization of 1H-Indol-2-yl Propargyl Benzoates to 7H-Benzo[c]carbazoles.

A synthetic method for the efficient assembly of benzo[c]carbazole derivatives that relies on silica gel-activated benzoic acid-mediated cycloaromatization of 1H-indol-2-yl propargyl benzoates under atmospheric conditions is described. Robust with a variety of substitution patterns tolerated, the reaction provides a one-step strategy to construct a member of the N-heterocycles family in good to excellent yields. A tentative mechanism is proposed in which the cycloaromatization process is thought to involve a Brønsted acid-mediated formal 1,3-acyloxy migration/6π-electrocyclization pathway.