Russell J. Linderman

Comparative metabolism of chloroacetamide herbicides and selected metabolites in human and rat liver microsomes.

Acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methyl-phenyl)-acetamide], alachlor [N-(methoxymethyl)-2-chloro-N-(2, 6-diethyl-phenyl)acetamide], butachlor [N-(butoxymethyl)-2-chloro-N-(2,6-diethyl-phenyl)acetamide], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] are pre-emergent herbicides used in the production of agricultural crops. These herbicides are carcinogenic in rats: acetochlor and alachlor cause tumors in the nasal turbinates, butachlor causes stomach tumors, and metolachlor causes liver tumors. It has been suggested that the carcinogenicity of these compounds involves a complex metabolic activation pathway leading to a DNA-reactive dialkylbenzoquinone imine. Important intermediates in this pathway are 2-chloro-N-(2,6-diethylphenyl)acetamide (CDEPA) produced from alachlor and butachlor and 2-chloro-N-(2-methyl-6-ethylphenyl)acetamide (CMEPA) produced from acetochlor and metolachlor. Subsequent metabolism of CDEPA and CMEPA produces 2,6-diethylaniline (DEA) and 2-methyl-6-ethylaniline (MEA), which are bioactivated through para-hydroxylation and subsequent oxidation to the proposed carcinogenic product dialkylbenzoquinone imine. The current study extends our earlier studies with alachlor and demonstrates that rat liver microsomes metabolize acetochlor and metolachlor to CMEPA (0.065 nmol/min/mg and 0.0133 nmol/min/mg, respectively), whereas human liver microsomes can metabolize only acetochlor to CMEPA (0.023 nmol/min/mg). Butachlor is metabolized to CDEPA to a much greater extent by rat liver microsomes (0.045 nmol/min/mg) than by human liver microsomes (< 0.001 nmol/min/mg). We have determined that both rat and human livers metabolize both CMEPA to MEA (0.308 nmol/min/mg and 0.541 nmol/min/mg, respectively) and CDEPA to DEA (0.350 nmol/min/mg and 0.841 nmol/min/mg, respectively). We have shown that both rat and human liver microsomes metabolize MEA (0.035 nmol/min/mg and 0.069 nmol/min/mg, respectively) and DEA (0.041 nmol/min/mg and 0.040 nmol/min/mg, respectively). We have also shown that the cytochrome P450 isoforms responsible for human metabolism of acetochlor, butachlor, and metolachlor are CYP3A4 and CYP2B6.

Regioselective synthesis of trifluoromethyl substituted quinolines from trifluoroacetyl acetylenes

Abstract Trifluoromethyl substituted quinolines have been prepared by 1, 2- or 1, 4- addition of anilines to trifluoroacetyl acetylenes followed by intramolecular acid catalyzed ring closure.

An efficient method for the synthesis of trifluoromethyl substituted heterocycles

Abstract Trifluoromethyl substituted pyrazoles and isoxazoles have been prepared regiospecifically in high yield from trifluoroacetyl acetylenes.

In vitro metabolism of alachlor by human liver microsomes and human cytochrome P450 isoforms

Alachlor (2-chloro-N-methoxymethyl-N-(2,6-diethylphenyl)acetamide) is a widely used pre-emergent chloroacetanilide herbicide which has been classified by the USEPA as a probable human carcinogen. The putative carcinogenic metabolite, 2,6-diethylbenzoquinone imine (DEBQI), is formed through a complex series of oxidative and non-oxidative steps which have been characterized in rats, mice, and monkeys but not in humans. A key metabolite leading to the formation of DEBQI is 2-chloro-N-(2,6-diethylphenyl)acetamide (CDEPA). This study demonstrates that male human liver microsomes are able to metabolize alachlor to CDEPA. The rate of CDEPA formation for human liver microsomes (0.0031 +/- 0.0007 nmol/min per mg) is significantly less than the rates of CDEPA formation for rat liver microsomes (0.0353+/-0.0036 nmol/min per mg) or mouse liver microsomes (0.0106 +/- 0.0007). Further, we have screened human cytochrome P450 isoforms 1A1, 1A2, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, and 3A4 and determined that human CYP 3A4 is responsible for metabolism of alachlor to CDEPA. Further work is necessary to determine the extent to which humans are able to metabolize CDEPA through subsequent metabolic steps leading to the formation of DEBQI.

An efficient procedure for the oxidation of fluorinated carbinols

Abstract The oxidation of di and trifluorocarbinols has been accomplished in high yields using the Dess-Martin periodane oxidant.

19F-NMR spectral evidence that 3-octylthio-1,1,1-trifluoropropan-2-one, a potent inhibitor of insect juvenile hormone esterase, functions as a transition state analog inhibitor of acetylcholinesterase

Abstract Fluoroketones have been developed as highly potent, specific inhibitors of insect juvenile hormone esterase. These compounds are believed to function as transition state analog inhibitors of the enzyme. Of the fluoroketones prepared, 3-octylthio-1,1,1-trifluoropropan-2-one has been extensively studied, yet no analysis of the actual mode of enzyme inhibition has been reported. A 19 F-NMR analysis of the inhibition of a hydrolytic enzyme, acetylcholinesterase, by 3-octylthio-1,1,1-trifluoropropan-2-one was carried out. Experiments with phosphorylated acetyl-cholinesterase determined that interaction of the fluoroketone with the enzyme is specific for the esteratic active site serine residue. The carbonyl moiety of the fluoroketone is required for binding and inhibition. The fluoroketone binds to the enzyme active site in a tetrahedral form, indicating that 3-octylthio-1,1,1-trifluoropropan-2-one does function as a transition state analog inhibitor of a hydrolytic enzyme.

The inhibition of insect juvenile hormone esterase by trifluoromethylketones: Steric parameters at the active site

Abstract A rationally designed structure-activity relationship study has been accomplished using trifluoromethylketone inhibitors of insect juvenile hormone esterase from the cabbage looper, Trichoplusia ni (Hubner) (Lepidoptera: Noctuidae). Several α- and α′-substituted derivatives of 3-octylthio-1,1,1-trifluoropropan-2-one have been prepared and assayed for inhibitory potency against juvenile hormone esterase. The results indicate that the sulfur/protein interaction does not occur in a sterically constrained environment. Substitution adjacent to sulfur did not dramatically effect activity. However, substitution adjacent to the carbonyl of the trifluoromethylketone moiety reduced inhibitory potency substantially, indicating that the active site region of juvenile hormone esterase which interacts with the carbonyl is restricted to rather small substrates. A small hydrophobic pocket near the active site has been identified and can serve to increase inhibitory potency by secondary binding of appropriate substituents. The present study has resulted in the preparation of two more effective in vitro inhibitors of juvenile hormone esterase than those previously reported. Evidence that there are two naturally occurring forms of juvenile hormone esterase has also been provided.

A reactivity umpolung route to cyclic homoenolate aldol products via α-alkoxyorganocuprate conjugate additions

Abstract Substituted α-alkoxyorganocuprate reagents readily undergo conjugate addition reactions with cyclic enones to provide homoaldol products.

The synthesis and stereoselective conjugate addition reactions of α-alkoxyorganocuprate reagents

Abstract α-Alkoxyorganocuprate reagents have been prepared from α-alkoxyorganostannanes. The cuprates undergo diastereoselective conjugate addition reactions with cyclohexenone with up to 8:92 selectivity. The effects of trimethylsilyl chloride on the chemical yields and the diastereoselectivity of the reaction are described.

A novel geminal diol as a highly specific and stable in vivo inhibitor of insect juvenile hormone esterase

Thio-containing and acetylenic trifluoromethyl ketones were potent inhibitors of insect juvenile hormone (JH) esterase with greater inhibitory activity than aliphatic and α,β-unsaturated homologs. Octylthio-1,1,1-trifluoropropan-2-one was the most potent inhibitor with the greatest equilibrium hydration constant in pure water. However, a keto/hydrate equilibrium was not necessary for JH esterase inhibition. The carbonyl tautomer of 1-octyl [1-(3,3,3-trifluoropropan-2,2- dihydroxy)] sulfone (OTPdOH-sulfone) was not detectable, and yet OTPdOH-sulfone was a potent in vitro inhibitor of JH esterase with an I50 of 1.2 nM. The mechanism of JH esterase inhibition by these compounds is discussed. OTPdOH-sulfone inhibited JH esterase with minimal activity toward insect 1-naphthyl acetate esterase and electric eel acetylcholinesterase. The inhibitor was also active in vivo, selective for JH esterase, and persistent for over 32 h. OTPdOH-sulfone when topically applied to larval and adult cabbage loopers, Trichoplusia ni, elicited juvenoid activity apparently because of the specific in vivo inhibition of JH metabolism. Arch. Insect Biochem. Physiol. 36:165–179, 1997.