Stereoselective synthesis and stereostructure-activity studies of P-menthane-3,8-diols as repellents of anopheles sp
Barasa, Stephen Super
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Malaria is by far the most devastating and deadly parasitic disease in the world. It is a public health problem in more than 90 countries inhabited by over 2.4 billion people (approximately 40% of the world's population). In an integrated and preventive approach to malaria control, methods that do not rely on mass application of insecticide but selectively target the malaria vector have become desirable. p-Menthane-3,8-diol is the active component of quwenlinq ; a mosquito repellent comparable in efficacy and duration to the leading mosquito repellent N, N-diethyl-m- toluamide (DEET). Quwenlinq, which means 'effective repeller of mosquitoes' is an extract from a Chinese plant, Eucalyptus citriodora. This study reveals that of the eight possible stereoisomers of p-menthane-3,8-diol, only four are resident in the plant. Enantiospecific as well as diastereoselective approaches to the laboratory synthesis of these diols are reported. GC-based chiral host-guest complexation was used to discriminate the otherwise unresolvable enantiomeric pairs. The Zimmermann-Traxler Model and stereoelectronic principles are used to explain the observed occurrence of Felkin Anh and anti-Felkin Anh products in different yields. Experimental data obtained compares favourably with spectroscopic as well as conformational analysis (semi-empirical calculations). Structure-activity studies of the natural and synthesized p-menthane-3,8-diols against the most efficient malaria vector, Anopheles gambiae, is reported.