Discovery of potent, nonsystemic apical sodium-codependent bile acid transporter inhibitors (Part 1)

Elevated plasma levels of low-density lipoprotein (LDL) cholesterol are a major risk factor for atherosclerosis leading to coronary artery disease (CAD), which remains the main cause of mortality in Western society. We believe that by preventing the reabsorption of bile acids, a minimally absorbed apical sodium-codependent bile acid transporter (ASBT) inhibitor would lower the serum cholesterol without the potential systemic side effects of an absorbed drug. A series of novel benzothiepines (3R,3R'-2,3,4,5-tetrahydro-5-aryl-1-benzothiepin-4-ol 1,1-dioxides) were synthesized and tested for their ability to inhibit the apical sodium dependent bile acid transport (ASBT)-mediated uptake of [(14)C]taurocholate (TC) in H14 cells. A 3R,4R,5R/3S,4S,5S racemate was found to have greater potency than the other three possible racemates. Addition of electron-donating groups such as a dimethylamino substituent at the 7 position greatly enhanced potency, and incorporation of a long-chain quaternary ammonium substituent on the 5-phenyl ring was useful in minimizing systemic exposure of this locally active ASBT inhibitor while also increasing water solubility and maintaining potency. The reported results describe the synthesis and SAR development of this benzothiepine class of ASBT inhibitors resulting in an 6000-fold improvement in ASBT inhibition with desired minimal systemic exposure of this locally acting drug candidate.

Discovery of Potent, Nonsystemic Apical Sodium-Codependent Bile Acid Transporter Inhibitors (Part 2)

In the preceding paper several compounds were reported as potent apical sodium-codependent bile acid transporter (ASBT) inhibitors. Since the primary site for active bile acid reabsorption is via ASBT, which is localized on the luminal surface of the distal ileum, we reasoned that a nonsystemic inhibitor would be desirable to minimize or eliminate potential systemic side effects of an absorbed drug. To ensure bioequivalency and product stability, it was also essential that we identify a nonhygroscopic inhibitor in its most stable crystalline form. A series of benzothiepines were prepared to refine the structure-activity relationship of the substituted phenyl ring at the 5-position of benzothiepine ring and to identify potent, crystalline, nonhygroscopic, and efficacious ASBT inhibitors with low systemic exposure.

Polymorphism and crystallization behavior of Abbott-79175, a second-generation 5-lipoxygenase inhibitor

The crystal polymorphism of Abbott-79175, a potent second-generation 5-lipoxygenase inhibitor, has been studied. Crystallization from an ethyl acetate/heptane system in which moisture content was not controlled and from an ethanol/water system produced a crystal form I, which by differential scanning calorimetry, thermogravimetric analysis, and Karl Fischer analysis was likely a hemihydrate. This hemihydrate form of the compound was demonstrated to reversibly dehydrate/hydrate with the use of low heat and vacuum followed by exposure to water vapor (100% relative humidity). The dehydrated version of I was designated IA. However, it was shown that a relative humidity approaching 100% was required for the water to re-enter the crystal structure. X-ray powder diffraction and solid state 13C NMR data on polycrystalline samples crystallized from seven single organic solvents suggested two nonsolvated forms of the compound, II and III. The heptane addition rate to a dry ethyl acetate solution of the drug was shown to greatly affect the crystal habit, the crystallite size, and specific surface area upon its precipitation. Solution calorimetry of forms I, IA, and II showed that I had the most endothermic heat of solution, with IA and II having lower values. Initial dissolution rates of compressed disks of these forms in water showed rates of IA > II approximately I. Considering all data, including evidence of conversion of II to I in aqueous suspension, it is suggested that the relative thermodynamic stability (at least when water was present) in decreasing order is I > II > IA, although I and II are similar energetically. The lower terminal dissolution rate for form IA was due to, in part, conversion to the less soluble Form I.