Engineered Imine Reductase for Asymmetric Synthesis of Dextromethorphan Key Intermediate.

(S)-1-(4-Methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquinoline ((S)-1-(4-methoxybenzyl)-OHIQ) is the key intermediate of the nonopioid antitussive dextromethorphan. In this study, (S)-IR61-V69Y/P123A/W179G/F182I/L212V (M4) was identified with a 766-fold improvement in catalytic efficiency compared with wide-type IR61 through enzyme engineering. M4 could completely convert 200 mM of 1-(4-methoxybenzyl)-3,4,5,6,7,8-hexahydroisoquinoline into (S)-1-(4-methoxybenzyl)-OHIQ in 77% isolated yield, with >99% enantiomeric excess and a high space-time yield of 542 g L-1 day-1, demonstrating a great potential for the synthesis of dextromethorphan intermediate in industrial applications.

Design, Synthesis, and Biological Evaluation of Phenol Bioisosteric Analogues of 3-Hydroxymorphinan.

The neuroprotective agent 3-hydroxymorphinan (3-HM) is a well-documented and highly safe therapeutic intervention for the inflammatory-related effects of Parkinson's disease (PD). However, the bioavailability of 3-HM is very low due to the rapid first-pass metabolism of the phenolic moiety. In the present study, we sought to improve the metabolic stability and overall pharmacokinetic profile of 3-HM. Based on an iterative design process that a suitably arranged heterocycle with an NH group would serve as the metabolically stable isostere of the phenolic group, we designed and synthesized two analogues of 3-HM. Benzimidazolone compound 8 (imidazolone-morphinan) was comparable in activity to 3-HM against lipopolysaccharide (LPS)-induced inflammatory responses in microglial BV2 cells and in vivo animal experiments (MPTP-induced PD mouse model). Moreover, the in vitro study showed that imidazolone-morphinan was non-toxic to microglia, indicating its high safety. Considering the favourable and unique preclinical profiles, compound 8 was nominated as a candidate for further clinical development.

Synthesis, in vitro and in vivo studies, and molecular modeling of N-alkylated dextromethorphan derivatives as non-competitive inhibitors of α3ß4 nicotinic acetylcholine receptor.

9 N-alkylated derivatives of dextromethorphan are synthesized and studied as non-competitive inhibitors of α3ß4 nicotinic acetylcholine receptors (nAChRs). In vitro activity towards α3ß4 nicotinic acetylcholine receptor is determined using a patch-clamp technique and is in the micromolar range. Homology modeling, molecular docking and molecular dynamics of ligand-receptor complexes in POPC membrane are used to find the mode of interactions of N-alkylated dextromethorphan derivatives with α3ß4 nAChR. The compounds, similarly as dextromethorphan, interact with the middle portion of α3ß4 nAChR ion channel. Finally, behavioral tests confirmed potential application of the studied compounds for the treatment of addiction.

Synthesis of potent sigma-1 receptor ligands via fragmentation of dextromethorphan.

Treatment of dextromethorphan 1 with various alkylating agents followed by base treatment led to Hoffman-type elimination reactions to produce a series of tricyclic derivatives, 6. These derivatives were characterized in vitro as sigma-1 receptor ligands.

EN-3231. Endo Pharmaceuticals.

Endo (which acquired Algos in July 2000) has developed EN-3231, a combination of morphine and dextromethorphan, for the treatment of moderate-to-severe chronic pain. In October 1998, the FDA accepted for filing the company's NDA submission on EN-3231, which was submitted in August 1998. However, in August 1999, Algos received a 'non-approvable' letter from the FDA for EN-3231. In September 2000, the company met with the FDA to discuss what information the FDA required in order to approve EN-3231. The FDA requested a second pivotal trial, which Endo initiated promptly. Endo hoped to file its supplement to the NDA during 2002.

Measurement of liver microsomal cytochrome p450 (CYP2D6) activity using [O-methyl-14C]dextromethorphan.

The activity of human liver microsomal cytochrome P4502D6 (CYP2D6) is readily estimated by following the O-demethylation of [O-methyl-14C]dextromethorphan. The basis of the assay is the quantitative measurement of [14C]formaldehyde (0.05-4.0 microM) after addition of NaOH to the microsomal incubates and extraction with methylene chloride. The assay is relatively simple, sensitive (limit of detection is approximately 5.0 pmol HCHO/h/mg microsomal protein) and does not require the use of HPLC or an internal standard. Formation of radiolabeled formaldehyde in human liver microsomes is linear for 20 min, up to a final protein concentration of 1.0 mg/ml. Furthermore, the O-demethylase activity in a panel of microsomes prepared from a series of human livers was significantly correlated with the immunochemically determined levels of CYP2D6 protein (r = 0.925, p < 0.001), and was inhibited (> 89%) by quinidine and lobeline. In addition, [O-methyl-14C]-dextromethorphan O-demethylation was exclusively catalyzed by cDNA-expressed CYP2D6 in microsomes prepared from human B-lymphoblast cells. The method is suitable for rapid screening of compounds as potential CYP2D6 cosubstrates and/or inhibitors.

Synthesis and evaluation of 3-substituted 17-methylmorphinan analogs as potential anticonvulsant agents.

Dextromethorphan (1,(+)-3-methoxy-17-methylmorphinan) demonstrates anticonvulsant activity in a variety of in vitro and in vivo models of convulsive action. It is well known that 1 is metabolized to its phenolic derivative dextrorphan (2) and this metabolite is also a potent anticonvulsant. A series of (+)-3-substituted-17-methylmorphinans, which are structurally similar to 1 but are either not expected to be metabolized to 2 or might do so at a reduced rate, as compared to 1, were prepared. Three analogs, 5 ((+)-3-amino-17-methylmorphinan), 14 ((+)-3-ethoxy-17-methylmorphinan), and 15 ((+)-3-(2-propoxy)-17-methylmorphinan) were found to possess potent anticonvulsant activity with full efficacy (ED50 25, 5.6, and 3.9 mg/kg, sc, respectively) in the rat supramaximal electroshock (MES) test. Binding potencies of these compounds to receptor sites labeled with [3H]dextromethorphan ([3H]1), in rat brain and guinea pig brain subcellular fractions, and [3H]thienylcyclohexylpiperidine (TCP) and [3H]glycine in rat brain, were determined. Most of the analogs displaced [3H]1 from its binding sites, with compounds 14 (IC50 0.42 microM) and 15 (IC50 0.88 microM) having equivalent potencies to 1 (IC50 0.59 microM), in rat brain, and no appreciable activity at the [3H]TCP or [3H]glycine-labeled sites. Compound 5 did not bind with appreciable activity to the [3H]1 site, in rat brain, but did bind to the [3H]TCP site with lower potency than the parent 1 (IC50 7.8 and 2.0 microM, respectively). The mechanism of anticonvulsant action of these agents is not clear although it appears that interaction at the [3H]1 sites may be involved.

N-Demethylation of dextromethorphan.

In addition to providing an efficient synthesis of 3-methoxymorphinan hydrochloride, the use of 2,2,2-trichloroethyl chloroformate in the N-demethylation of dextromethorphan led to the isolation of two novel zinc salts of 3-methoxymorphinan.