A structurally novel series of adenosine 5'-triphosphate-sensitive potassium (K(ATP)) channel openers is described. As part of our efforts directed toward identifying novel, bladder-selective potassium channel openers (KCOs) targeted for urge urinary incontinence (UUI), we found that bioisosteric replacement of the N-cyanoguanidine moiety of pinacidil (1, Figure 1) with a diaminocyclobutenedione template afforded squaric acid analogue 2, the prototype of a novel series of K(ATP) channel openers with unique selectivity for bladder smooth muscle in vivo. Further modification of the heterocyclic ring to give substituted aryl derivatives (3) afforded potent KCOs that possessed the desired detrusor selectivity when administered orally. The effects of these potassium channel agonists on bladder contractile function was studied in vitro using isolated rat detrusor strips. Potent relaxants were evaluated in vivo in a rat model of bladder instability. Lead compounds were evaluated concomitantly in normotensive rats for their effects on mean arterial blood pressure (MAP) and heart rate as a measure of in vivo bladder selectivity. (R)-4-[3,4-Dioxo-2-(1,2, 2-trimethyl-propylamino)-cyclobut-1-enylamino]-3-ethyl-benzo nitrile (79) met our potency and selectivity criteria and represents an attractive development candidate for the treatment of UUI. Electrophysiological studies using isolated rat bladder detrusor myocytes have demonstrated that compound 79 produces significant hyperpolarization which is glyburide-reversed, thus consistent with the activation of K(ATP). The design, synthesis, structure-activity relationships (SAR), and pharmacological activity associated with this series of novel KCOs will be discussed.

A novel series of benzylamine, potassium channel openers (KCOs) is presented as part of our program toward designing new, bladder-selective compounds for the treatment of urge urinary incontinence (UUI). We have found that the in vitro potency of (R)-4-[3,4-dioxo-2-(1,2, 2-trimethyl-propylamino)-cyclobut-1-enylamino]-3-ethyl-benzo nitrile 1 in the relaxation of precontracted rat detrusor strips can also be obtained with cyanobenzylamine derivative 4 (IC(50) = 0.29 microM) (Figure 3). Addition of a 2-Cl substituted benzylamine moiety and changing the alkylamino substituent of 4 to a t-Bu amine gives 31 (IC(50) = 0.14 microM)-a compound with similar in vitro potency as 4 as well as relaxant activity on bladder smooth muscle in vivo when administered orally (31, ED(50) = 3 mg/kg) in a rodent model of bladder instability. Further modifications, particularly the replacement of the t-Bu amino substituent with a tert-amylamine, gave a similarly active compound 60 (IC(50) = 0.10 microM) which shows excellent in vivo efficacy (ED(50) = 0.6 mg/kg). Moreover, 60, 3-(2,4-dichloro-6-methyl-benzylamino)-4-(1, 1-dimethyl-propylamino)-cyclobut-3-ene-1,2-dione (WAY-151616), shows excellent tissue selectivity for bladder K channels over arterial tissue (60, MAP ED(20) = 100 mg/kg; selectivity: MAP ED(20)/bladder ED(50) = 166). Other manipulations of the benzylamino cyclobutenediones, acylation of the benzylamine, conversion of the benzylamine substituent to a benzamide, homologation of the benzylamine to a phenethylamine, and incorporation of a methyl group at the benzyl carbon, all led to substantial loss of in vitro activity, although some in vivo activity was maintained in the acylated analogues. Compound 60 represents an attractive candidate for development in the treatment of UUI.

Recently, we required a variety of chiral R-methylamines for SAR studies in the course of drug discovery. It has been known that an alkyl substituent adjacent to a heteroatom can alter the biological activity and metabolic pathway in a related compound series. 1 Our SAR studies required a range of chiral intermediates possessing this single structural trait. We therefore undertook a program to identify an efficient synthesis of these branched amines.We envisioned the use of R-amino acids as starting materials for the preparation of R-methylamines. The wide availability of optically pure R-amino acids renders them an excellent starting material for this transformation. Indeed, there are a few procedures in the literature that describe this conversion. 2-4 For our purposes we needed a procedure that was compatible with a wide range of functionality and adaptable to larger scale. We also required that the R-methylamines be prepared in enantiopure form. Bloom 2 and Yamada 4 have reported low-yielding routes for a single amino acid. Neither route was adaptable to a wide range of functional groups. We were unable to reproduce the procedure reported by Donner. 3 This Note describes an efficient and general method for the preparation of enantiomerically pure R-methylamines from corresponding chiral amino acids.To investigate the effect of fluorine atom substitution on alkylamine groups for a discovery program in potassium channel modulation, we required 2-fluoro-1,2-dimethylpropylamine, 6. 5 Since DL-3-fluorovaline, 1, is commercially available, our synthetic studies were initiated using this racemic amino acid. As shown in Scheme 1, DL-3-fluorovaline, 1, was reduced to amino alcohol 2 cleanly using lithium borohydride/trimethylsilyl chloride. 6 The amino group was protected as a tert-butyl carbamate to give 3 using di-tert-butyl dicarbonate. 7 The transformation of the carbinol into a methyl group was carried out in two steps. It was found that the primary alcohol group was easily replaced by an iodide atom using the method of Caputo to afford 4. 8 Reduction of the carbon-iodine bond to give 5 was accomplished by catalytic hydrogenation over Pearlman's catalyst. 9 Removal of the BOC protecting group was straightforward using trifluoroacetic acid. 10 The above procedure, while efficient, required further refinement for the following reasons: (a) the need to determine whether there was racemization of the R-carbon of chiral amino acids during this transformation; (b) the catalytic hydrogenation step was not general and did not work well for several other amino acids; (c) flash chromatography was required to purify two steps of the original sequence. We wanted to design a route that avoided tedious chromatography and improved the yields for individual steps to greater than 85%, so refinement was necessary.Optimization studies of our original sequence were carried out using both D-and L-phenylalanine. The reduction of amino acid 7 to amino alcohol 8, using LiBH 4 / TMSCl, proceeded cleanly and in high yield (Scheme 2). I...

Acyl carrier protein synthase (AcpS) catalyzes the transfer of the 4'-phosphopantetheinyl group from the coenzyme A to a serine residue in acyl carrier protein (ACP), thereby activating ACP, an important step in cell wall biosynthesis. The structure-based design of novel anthranilic acid inhibitors of AcpS, a potential antibacterial target, is presented. An initial high-throughput screening lead and numerous analogues were modeled into the available AcpS X-ray structure, opportunities for synthetic modification were identified, and an iterative process of synthetic modification, X-ray complex structure determination with AcpS, biological testing, and further modeling ultimately led to potent inhibitors of the enzyme. Four X-ray complex structures of representative anthranilic acid ligands bound to AcpS are described in detail.

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