Synthesis of Insecticidal Mono- and Diacylhydrazines for Disruption of K+ Voltage-Gated Channels, and Elucidation of Regiochemistry and Conformational Isomerism by NMR Spectroscopy and Computation
| dc.contributor.author | Clements, Joseph Shelby II | en |
| dc.contributor.committeechair | Carlier, Paul R. | en |
| dc.contributor.committeemember | Kingston, David G. I. | en |
| dc.contributor.committeemember | Tanko, James M. | en |
| dc.contributor.committeemember | Yee, Gordon T. | en |
| dc.contributor.department | Chemistry | en |
| dc.date.accessioned | 2017-06-06T08:01:08Z | en |
| dc.date.available | 2017-06-06T08:01:08Z | en |
| dc.date.issued | 2017-06-05 | en |
| dc.description.abstract | Based on the success of diacyl-tert-butylhydrazines RH-5849 and RH-1266 in controlling agricultural crop pests, we endeavored to synthesize our own diacylbenzyl- and arylhydrazine derivatives for use against the malaria vector Anopheles gambiae. In the process of producing a library of compounds for assay against An. gambiae, it became clear that employing regioselective acylation techniques (in molecules that feature two nucleophilic, acyclic nitrogen atoms α to one another) would be imperative. Synthesis of the library derivatives proceeded rapidly and after topical assay, we found three compounds that were more toxic than the RH-series leads. One of the three displayed an LD50 value of half that of RH-1266, though patch clamp assay concluded that toxicity was not necessarily linked to inhibition of mosquito K+ channel Kv2.1. The acylation of monoarylhydrazines appears simple, but its regioselectivity is poorly understood when assumed as a function of basicity correlating to nucleophilic strength. We determined the ratio of the rate constants for distal to proximal N-acylation using 19F NMR spectroscopic analysis of reactions of 4-fluorophenylhydrazine with limiting (0.2 equiv) acylating agent in the presence of various bases. Acid anhydrides gave consistent preference for distal acylation. The selectivity of acylation by acyl chlorides when using pyridine gives strong distal preference, whereas use of triethylamine or aqueous base in conjunction with aroyl chlorides showed a moderate preference for proximal acylation. This observation yielded a convenient one-step method to synthesize proximal aroylarylhydrazines in yields comparable or superior to that provided by the standard three-step literature approach. Combined with NMR evidence of the distal nitrogen as the unambigiously stronger base of the two nitrogens, we propose a single electron transfer mechanism that predicts the regiochemistry of arylhydrazines toward acylating agents better than the nucleophilicity model based on pKa values. While synthesizing the acylhydrazine library for assay against An. gambiae, NMR spectroscopy revealed rotational isomerisms of two types: chiral helicity (M)/(P) and acyl (E)/(Z)-isomerism due to hindered rotation. Variable temperature NMR allowed the measurement of N-N bond rotational barriers, as well as estimate the barrier of (E)/(Z) interconversion. We obtained the X-ray crystal structures of four diacylhydrazines to test this hypothesis and revealed both the twist conformation around the N-N bond axis and (E)/(Z)-isomerism around the proximal acyl group. Computation (which agreed with the crystal structures) allowed us to estimate which (E)/(Z)-isomers were most likely being observed in solution at room temperature by NMR spectroscopy. In addition, we were able to calculate transition structures corresponding to N-N bond rotational barriers of (E,Z)- and (Z,Z)-isomers of model molecules and rationalize the difference in coalescence temperatures between (E,Z)- and (Z,Z)-isomers. | en |
| dc.description.abstractgeneral | Herein we present the work of both synthesizing and characterizing the mosquitocidal and chemical properties of acylhydrazines. Part of the challenge of working with hydrazines comes in part from deceptive comparisons to amines and ammonia; hydrazine is as different from ammonia as hydrogen peroxide is from water. We were successful in identifying effective synthetic techniques to obtain our desired acylhydrazines reliably and managed to discover compounds that were better at eliminating <i>Anopheles gambiae</i> (the african malaria mosquito vector) than lead compounds from previous researchers. In the process of making the library of compounds for mosquito testing, we explored hydrazine reactivity toward acylating agents in a direct and deeper way than previous work, as well as their dynamic structural features. We employed a battery of techniques, including NMR, X-ray crystallography, and computational molecular modeling to understand these molecules and possibly contribute insight into their biochemical efficacy. | en |
| dc.description.degree | Ph. D. | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:11478 | en |
| dc.identifier.uri | http://hdl.handle.net/10919/77918 | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | Hydrazine | en |
| dc.subject | acylation | en |
| dc.subject | α-effect | en |
| dc.subject | regioselectivity | en |
| dc.subject | hydrazide | en |
| dc.subject | voltage-gated | en |
| dc.subject | (E)-/(Z)- | en |
| dc.subject | 19F NMR | en |
| dc.subject | single electron transfer (SET) | en |
| dc.subject | rotational barrier | en |
| dc.subject | N-N bond rotation | en |
| dc.subject | rotational isomerism | en |
| dc.subject | helicity | en |
| dc.subject | transition state | en |
| dc.subject | dihedral angle | en |
| dc.title | Synthesis of Insecticidal Mono- and Diacylhydrazines for Disruption of K+ Voltage-Gated Channels, and Elucidation of Regiochemistry and Conformational Isomerism by NMR Spectroscopy and Computation | en |
| dc.type | Dissertation | en |
| thesis.degree.discipline | Chemistry | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Ph. D. | en |
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