R¹ is selected from the group consisting of methoxycarbonyl, ethoxycarbonyl, t-butoxycarbonyl, isopropyl, n-butyl, t-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, benzyl, phenyl, tetrahydronaphthyl, indolyl, tetrahydrofuryl, pyrrolidinyl, and morpholinyl, wherein R¹ is optionally substituted by one or more substituents selected from the group consisting of methyl, ethyl, propyl, bromo, fluoro, chloro, and keto;

R² is selected from the group consisting of methyl, phenyl, biphenyl, naphthyl, tetrahydrofuryl, pyrrolidinyl, morpholinyl, piperidyl, thienyl, pyrrolyl, and pyridyl, or R² and R⁸ together with the atom to which they are both attached form a piperidyl or cyclohexyl group, wherein R² or the piperidyl or cycohexyl group formed with R⁸ is optionally substituted by one or more substituents selected from the group consisting of methoxy, ethoxy, methyl, ethyl, isopropyl, isobutyl, methylphenoxy, methylthio, phenylethenyl, benzyloxy, phenylethoxy, benzyl, phenoxy, cyano, fluoro, chloro, bromo, trifluoromethyl, trifluoromethylphenyl, dichlorophenoxy, imidazole, benzodioxole, hydroxy, hydroxyethoxy, N-(methylcarbonyl)amino, and nitro;

R⁴, R⁵, R⁶, and R⁷ are independently selected from the group consisting of hydrogen, methyl, ethyl, n-propyl, isopropyl, fluoro, chloro, and bromo;

R⁸ is hydrogen or alkyl; and

R^10a, R^10b, R^10c, R^10d, and R^10e are independently selected from the group consisting of hydrogen, methyl, hydroxy, and methoxy.