FLESINOXAN HYDROCHLORIDE

Protein engineering of toluene 4-monooxygenase of Pseudomonas mendocina KR1 for synthesizing 4-nitrocatechol from nitrobenzene

After discovering that toluene 4-monooxygenase (T4MO) of Pseudomonas mendocina KR1 oxidizes nitrobenzene to 4-nitrocatechol, albeit at a very low rate, this reaction was improved using directed evolution and saturation mutagenesis. Screening 550 colonies from a random mutagenesis library generated by error-prone PCR of tmoAB using Escherichia coli TG1/pBS(Kan)T4MO on agar plates containing nitrobenzene led to the discovery of nitrocatechol-producing mutants. One mutant, NB1, contained six amino acid substitutions (TmoA Y22N, I84Y, S95T, I100S, S400C; TmoB D79N). It was believed that position I100 of the alpha subunit of the hydroxylase (TmoA) is the most significant for the change in substrate reactivity due to previous results in our lab with a similar enzyme, toluene ortho-monooxygenase of Burkholderia cepacia G4. Saturation mutagenesis at this position resulted in the generation of two more nitrocatechol mutants, I100A and I100S; the rate of 4-nitrocatechol formation by I100A was more than 16 times higher than that of wild-type T4MO at 200 microM nitrobenzene (0.13 +/- 0.01 vs. 0.008 +/- 0.001 nmol/min.mg protein). HPLC and mass spectrometry analysis revealed that variants NB1, I100A, and I100S produce 4-nitrocatechol via m-nitrophenol, while the wild-type produces primarily p-nitrophenol and negligible amounts of nitrocatechol. Relative to wild-type T4MO, whole cells expressing variant I100A convert nitrobenzene into m-nitrophenol with a Vmax of 0.61 +/- 0.037 vs. 0.16 +/- 0.071 nmol/min.mg protein and convert m-nitrophenol into nitrocatechol with a Vmax of 3.93 +/- 0.26 vs. 0.58 +/- 0.033 nmol/min.mg protein. Hence, the regiospecificity of nitrobenzene oxidation was changed by the random mutagenesis, and this led to a significant increase in 4-nitrocatechol production. The regiospecificity of toluene oxidation was also altered, and all of the mutants produced 20% m-cresol and 80% p-cresol, while the wild-type produces 96% p-cresol. Interestingly, the rate of toluene oxidation (the natural substrate of the enzyme) by I100A was also higher by 65% (7.2 +/- 1.2 vs. 4.4 +/- 0.3 nmol/min mg protein). Homology-based modeling of TmoA suggests reducing the size of the side chain of I100 leads to an increase in the width of the active site channel, which facilitates access of substrates and promotes more flexible orientations.

Integrated bioproduction and extraction of 3-methylcatechol

Pseudomonas putida MC2 is a solvent-tolerant strain that accumulates 3-methylcatechol. In aqueous media, 10 mM of 3-methylcatechol was produced and production was limited by 3-methylcatechol toxicity to the biocatalyst. Production levels increased by introduction of a second, organic phase that provides the substrate toluene and extracts the product from the culture medium. Octanol was shown to be an appropriate second phase with respect to tolerance of the strain for this solvent and with respect to partitioning of both substrate and product. Per unit of overall reactor volume (octanol and water), best results were obtained with 50% (v/v) of octanol: an overall 3-methylcatechol concentration of 25 mM was reached with 96% of the product present in the octanol phase. These product concentrations are much higher than in aqueous media without organic solvent, indicating that biocatalysis in an organic/aqueous two-phase system is an improved set-up for high production levels of 3-methylcatechol.

Preclinical pharmacology of B-20991, a 5-HT1A receptor agonist with anxiolytic activity

The purpose of this study was to characterize the pharmacological effects of 2-[[4-(o-methoxyphenyl)piperazin-1-yl]methyl]-1,3-dioxoperhydro imidazo[1,5-a]pyridine (B-20991) by using several biochemical and behavioral assays. Results of binding studies showed that B-20991 binds with high affinity to the 5-HT1A receptor (Ki = 31.7 +/- 1.7 nM), moderate affinity to 5-HT3 receptor (Ki = 269.4 +/- 23.2 nM) and low affinity (Ki > 1000) to 5-HT2A receptor, dopamine D2 receptor, benzodiazepine receptors and alpha1-adrenoceptor. The administration of B-20991 produced a dose and time related decrease in mouse rectal temperature, increased both lower lip retraction and flat body posture behavioral scores in rat, decreased 5-hydroxytryptamine (5-HT, serotonin) neuronal activity in mouse hypothalamus, and did not alter dopamine neuronal activity nor locomotor activity. The anxiolytic activity of B-20991 was assessed by using both the social interaction and light/dark box tests. The results of these tests indicated that B-20991 caused a dose-related increase in the social interaction and light/dark box behavioral scores. Taken together, these results suggest that B-20991 is a 5-HT1A receptor agonist that exhibits anxiolytic activity.

S 14671: a novel naphthylpiperazine 5-HT1A agonist of high efficacy and exceptional in vivo potency

The novel, naphthylpiperazine 5-HT1A agonist, S 14671 (4-[(thenoyl-2)aminoethyl]-1-(7-methoxynaphtylpiperazine], displayed very high affinity for 5-HT1A binding sites (pKi = 9.3) as compared to the serotonin (5-HT)1A agonists, 8-OH-DPAT (9.2) and (+)-flesinoxan (8.7) and the 5-HT1A partial agonists, buspirone (7.9) and BMY 7378 (8.8). In vivo, S 14671 induced the typical 5-HT1A agonist-induced responses of hypothermia and spontaneous tail-flicks at doses as low as greater than or equal to 5 micrograms/kg s.c. and greater than or equal to 40 micrograms/kg s.c., respectively. In each test, it was about 10-fold more potent than 8-OH-DPAT and 100-fold more potent than (+)-flesinoxan and buspirone. The actions of S 14671 could be blocked by BMY 7378 and the 5-HT1A receptor antagonist, (-)-alprenolol, but not by the 5-HT1C/2 receptor antagonist, ritanserin, nor the 5-HT3 receptor antagonist, ICS 205930. Thus, S 14671 is a novel 5-HT1A ligand of high efficacy and exceptional in vivo potency.

Agonist action at 5-HT1C receptors facilitates 5-HT1A receptor-mediated spontaneous tail-flicks in the rat

In rats lightly restrained in plastic cylinders, subcutaneous administration of the selective, high efficacy 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), induced spontaneous tail-flicks, that is, tail-flicks in the absence of extraneous stimulation. The putative 5-HT1B receptor agonist, CGS 12066B, the mixed 5-HT1B/1C receptor agonists, 1-((3-(trifluoromethyl)phenyl]piperazine (TFMPP) and 1-(3-chlorophenyl)piperazine (mCPP), the 5-HT1C/2 receptor agonist, [+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and the 5-HT1B/1C/2 receptor agonist, quipazine, did not, in contrast, elicit tail-flicks when applied alone. However, TFMPP, mCPP, DOI and quipazine, but not CGS 12066B, each potentiated the action of 8-OH-DPAT. Further, in the presence of TFMPP, mCPP and DOI, the dose-response curve for the induction of tail-flicks by 8-OH-DPAT was both steeper and shifted to the left. Tail-flicks induced by another high efficacy 5-HT1A receptor agonist, lisuride, were also enhanced by TFMPP, mCPP and DOI. The 5-HT1A receptor partial agonists, buspirone and (+/-)-flesinoxan, evoked tail-flicks only in the presence of TFMPP, mCPP or DOI. The mixed 5-HT1C/2 receptor antagonists, ritanserin and ICI 169,369, did not modify the action of 8-OH-DPAT alone but abolished the potentiation of 8-OH-DPAT-induced tail-flicks by DOI and TFMPP. Further, the selective 5-HT1A receptor antagonist, BMY 7378, blocked tail-flicks induced by both 8-OH-DPAT alone and 8-OH-DPAT plus DOI or TFMPP. A common property of those drugs potentiating 8-OH-DPAT-induced tail-flicks is an agonist action at 5-HT1C receptors and the data indicate that it is this mechanism which underlies the facilitation of tail-flicks.