Synthesis and Structure-Activity Relationships of 2,5-Dimethoxy-4-Substituted Phenethylamines and the Discovery of CYB210010: A Potent, Orally Bioavailable and Long-Acting Serotonin 5-HT2 Receptor Agonist

Structure-activity studies of 4-substituted-2,5-dimethoxyphenethylamines led to the discovery of 2,5-dimethoxy-4-thiotrifluoromethylphenethylamines, including CYB210010, a potent and long-acting serotonin 5-HT2 receptor agonist. CYB210010 exhibited high agonist potency at 5-HT2A and 5-HT2C receptors, modest selectivity over 5-HT2B, 5-HT1A, 5-HT6, and adrenergic α2A receptors, and lacked activity at monoamine transporters and over 70 other proteins. CYB210010 (0.1-3 mg/kg) elicited a head-twitch response (HTR) and could be administered subchronically at threshold doses without behavioral tolerance. CYB210010 was orally bioavailable in three species, readily and preferentially crossed into the CNS, engaged frontal cortex 5-HT2A receptors, and increased the expression of genes involved in neuroplasticity in the frontal cortex. CYB210010 represents a new tool molecule for investigating the therapeutic potential of 5-HT2 receptor activation. In addition, several other compounds with high 5-HT2A receptor potency, yet with little or no HTR activity, were discovered, providing the groundwork for the development of nonpsychedelic 5-HT2A receptor ligands.

Mosquito Acetylcholinesterase as a Target for Novel Phenyl-Substituted Carbamates

New insecticides are needed for control of disease-vectoring mosquitoes and this research evaluates the activity of new carbamate acetylcholinesterase (AChE) inhibitors. Biochemical and toxicological characterization of carbamates based on the parent structure of terbam, 3-tert-butylphenyl methylcarbamate, was performed. In vitro enzyme inhibition selectivity (Anopheles gambiae versus human) was assessed by the Ellman assay, as well as the lethality to whole insects by the World Health Organization (WHO) paper contact assay. Bromination at the phenyl C6 position increased inhibitory potency to both AChEs, whereas a 6-iodo substituent led to loss of potency, and both halogenations caused a significant reduction of mosquitocidal activity. Similarly, installation of a hexyl substituent at C6 drastically reduced inhibition of AgAChE, but showed a smaller reduction in the inhibition of hAChE. A series of 4-carboxamido analogs of the parent compound gave reduced activity against AgAChE and generally showed more activity against hAChE than AgAChE. Replacement of the 3-t-buyl group with CF₃ resulted in poor anticholinesterase activity, but this compound did have measurable mosquitocidal activity. A series of methyl- and fluoro- analogs of 3-trialkylsilyl compounds were also synthesized, but unfortunately resulted in disappointing activity. Finally, a series of sulfenylated proinsecticides showed poor paper contact toxicity, but one of them had topical activity against adult female Anopheles gambiae. Overall, the analogs prepared here contributed to a better understanding of carbamate structure–activity relationships (SAR), but no new significant leads were generated.

Effects of Microclimate Condition Changes Due to Land Use and Land Cover Changes on the Survivorship of Malaria Vectors in China-Myanmar Border Region

In the past decade, developing countries have been experiencing rapid land use and land cover changes, including deforestation and cultivation of previously forested land. However, little is known about the impact of deforestation and land-use changes on the life history of malaria vectors and their effects on malaria transmission. This study examined the effects of deforestation and crop cultivation on the adult survivorship of major malaria mosquitoes, Anopheles sinensis and An. minimus in the China-Myanmar border region. We examined three conditions: indoor, forested, and banana plantation. Mean survival time of An. sinensis in banana plantation environment was significantly longer than those in forested environment, and mosquitoes exhibited the longest longevity in the indoor environment. This pattern held for both males and females, and also for An. minimus. To further test the effect of temperature on mosquito survival, we used two study sites with different elevation and ambient temperatures. Significantly higher survivorship of both species was found in sites with lower elevation and higher ambient temperature. Increased vector survival in the deforested area could have an important impact on malaria transmission in Southeast Asia. Understanding how deforestation impacts vector survivorship can help combat malaria transmission.

Mosquitocidal carbamates with low toxicity to agricultural pests: an advantageous property for insecticide resistance management

BACKGROUND

Insecticide resistance in the malaria mosquito Anopheles gambiae is well documented, and widespread agricultural use of pyrethroids may exacerbate development of resistance when pyrethroids are used in vector control. We have developed carbamate anticholinesterases that possess a high degree of An. gambiae:human selectivity for enzyme inhibition. The purpose of this study was to assess the spectrum of activity of these carbamates against other mosquitoes and agricultural pests.

RESULTS

Experimental carbamates were potent inhibitors of mosquito acetylcholinesterases, with IC50 values in the nanomolar range. Similar potencies were observed for Musca domestica and Drosophila melanogaster enzymes. Although meta-substituted carbamates were potent inhibitors, two ortho-substituted carbamates displayed poor enzyme inhibition (IC50 ≥ 10(-6)  M) in honey bee (Apis mellifera), Asian citrus psyllid (Diaphorina citri) and lepidopteran agricultural pests (Plutella xylostella and Ostrinia nubilalis). Enzyme inhibition results were confirmed by toxicity studies in caterpillars, where the new carbamates were 2-3-fold less toxic than propoxur and up to tenfold less active than bendiocarb, indicating little utility of these compounds for crop protection.

CONCLUSION

The experimental carbamates were broadly active against mosquito species but not agricultural pests, which should mitigate selection for mosquito insecticide resistance by reducing agricultural uses of these compounds. © 2014 Society of Chemical Industry.

Aryl methylcarbamates: potency and selectivity towards wild-type and carbamate-insensitive (G119S) Anopheles gambiae acetylcholinesterase, and toxicity to G3 strain An. gambiae

New carbamates that are highly selective for inhibition of Anopheles gambiae acetylcholinesterase (AChE) over the human enzyme might be useful in continuing efforts to limit malaria transmission. In this report we assessed 34 synthesized and commercial carbamates for their selectivity to inhibit the AChEs found in carbamate-susceptible (G3) and carbamate-resistant (Akron) An. gambiae, relative to human AChE. Excellent correspondence is seen between inhibition potencies measured with carbamate-susceptible mosquito homogenate and purified recombinant wild-type (WT) An. gambiae AChE (AgAChE). Similarly, excellent correspondence is seen between inhibition potencies measured with carbamate-resistant mosquito homogenate and purified recombinant G119S AgAChE, consistent with our earlier finding that the Akron strain carries the G119S mutation. Although high (100- to 500-fold) WT An. gambiae vs human selectivity is observed for several compounds, none of the carbamates tested potently inhibits the G119S mutant enzyme. Finally, we describe a predictive model for WT An. gambiae tarsal contact toxicity of the carbamates that relies on inhibition potency, molecular volume, and polar surface area.

Re-engineering aryl methylcarbamates to confer high selectivity for inhibition of Anopheles gambiae versus human acetylcholinesterase

To identify potential human-safe insecticides against the malaria mosquito we undertook an investigation of the structure-activity relationship of aryl methylcarbamates inhibitors of acetylcholinesterase (AChE). Compounds bearing a β-branched 2-alkoxy or 2-thioalkyl group were found to possess good selectivity for inhibition of Anopheles gambiae AChE over human AChE; up to 530-fold selectivity was achieved with carbamate 11d. A 3D QSAR model is presented that is reasonably consistent with log inhibition selectivity of 34 carbamates. Toxicity of these compounds to live Anopheles gambiae was demonstrated using both tarsal contact (filter paper) and topical application protocols.

Access to "Friedel-Crafts-restricted" tert-alkyl aromatics by activation/methylation of tertiary benzylic alcohols

Herein we describe a two-step protocol to prepare m-tert-alkylbenzenes. The appropriate tertiary benzylic alcohols are activated with SOCl(2) or concentrated HCl and then treated with trimethylaluminum, affording the desired products in 68-97% yields (22 examples). This reaction sequence is successful in the presence of a variety of functional groups, including acid-sensitive and Lewis-basic groups. In addition to t-Bu groups, 1,1-dimethylpropyl and 1-ethyl-1-methylpropyl groups can also be installed using this method.