Asymmetric synthesis of both enantiomers of α,α-difluoroeldanolide: An interesting property of their biological activity

Synthesis of Selectively gem-Difluorinated Molecules; Chiral gem-Difluorocyclopropanes via Chemo-Enzymatic Reaction and gem-Difluorinated Compounds via Radical Reaction

The incorporation of fluorine atoms into an organic compound can alter the chemical reactivity or biological activity of the resulting compound due to the strong electron withdrawing nature of the fluorine atom. We have synthesized many original gem-difluorinated compounds and described the results in four sections. The first section describes the synthesis of optically active-gem-difluorocyclopropanes via the chemo-enzymatic reaction; we applied these compounds to liquid crystalline molecules, then further discovered a potent DNA cleavage activity for the gem-difluorocyclopropane derivatives. The second section describes the synthesis of selectively gem-difluorinated compounds via a radical reaction; we synthesized fluorinated analogues of a sex pheromone of the male African sugarcane borer, Eldana saccharina, and used the compounds as proof for investigating the origin of pheromone molecule recognition on the receptor protein. The third involves the synthesis of 2,2-difluorinated-esters by visible light-driven radical addition of 2,2-difluoroacetate with alkenes or alkynes in the presence of an organic pigment. The last section describes the synthesis of gem-difluorinated compounds via the ring-opening of gem-difluorocyclopropanes. We further developed a novel method of synthesizing gem-difluorohomoallylic alcohols via the ring-opening of gem-difluorocyclopropane and aerobic oxidation by photo-irradiation in the presence of an organic pigment. Since gem-difluorinated compounds that were prepared by the present method have two olefinic moieties with a different reactivity at the terminal position, we accomplished the synthesis of four types of gem-difluorinated cyclic alkenols via the ring-closing-metathesis (RCM) reaction.

Possible origin of modified EAG activity by point-fluorination of insect pheromones

Fluorine closely mimics the steric requirement of hydrogen at enzyme receptor sites, but its strong electronegativity significantly alters the reactivity of neighboring centers. Therefore, point-fluorination of biologically active molecules is an important technology with which to investigate the relationship between a biologically active compound with a receptor protein. We synthesized point-fluorinated pheromone analogues of eldanolide and measured their biological activity by electroantennography (EAG) to understand the importance of conformation in the specificity of ligand recognition by the olfactory receptor. By comparing EAG activities and conformational analysis of these molecules using density functional theory calculations, significant differences were found in the population of preferable conformers between EAG-active compounds and EAG-inactive compounds. Based on these results, we propose a working hypothesis for the possible origin of the diversity of relationship between enantiomer and activity in pheromone perception response. These results obtained in the investigation of the mechanism of chemical communication through pheromone molecules among insects should be useful to expand the horizons of medicinal chemists.

The Influence of Fluorinated Molecules (Semiochemicals and Enzyme Substrate Analogues) on the Insect Communication System

Can the introduction of fluorine atoms affect the bioactivity of natural semiochemicals? Can fluorine contribute in the creation of specific enzyme inhibitors to interrupt or disrupt the insect communication system? The first step for the bioactivity of a molecule is interaction with the biological sensor. Hydrogen and fluorine are almost bioisosteric and the receptor site of the enzyme can still recognize and accept the fluoro analogue of its natural substrate. However, the peculiar electronegativity of the fluorine atom can affect the binding, absorption, and transport of the molecule. The differences in the molecule's electronic properties can lead to differences in the chemical interactions between the receptor and the fluorinated substrate. Fluorine introduction can modify the metabolic stability and pathway of the semiochemicals in many different ways. Fluorinated analogues can show synergism, inhibition, or hyperagonism effects on insect behaviors, that is, the activity of the nonfluorinated parent compounds can be mimicked, lost, or increased. In any case, the fluorinated molecules can interact with the bioreceptors in a new and disrupting way. The semiochemicals are olfactory substances: fluorine can affect their volatility or smell. Production of semiochemicals from exogenous substances, perception at antennal receptors, and processing of biological responses are the main steps of communication among insects. In the production step, the fluorinated molecules can interact with enzymes that catalyze the biosynthesis of the natural pheromones. In the perception step, fluorinated semiochemicals can interact with the olfactory receptor cells; this often leads to totally unpredictable behaviors. Fluorinated molecules have been developed as probes to elucidate the complex chemorecognition processes of insects. Many of these molecules have been tested to find highly effective behavior-modifying chemicals. New analogues have been synthesized to investigate the metabolic pathway of a pheromone molecule and many of them are promising disrupting agents. Despite such titanic research efforts, the results have often been random, rational trends in the induced behaviors have sometimes been impossible to find, and practical applications of the fluorinated semiochemicals are still uncertain.

Systematic Synthesis of Multifluorinated alpha,alpha-Difluoro-gamma-lactones through Intramolecular Radical Cyclization

Carbon radicals from allyl O-(trimethylsilyl)-alpha-bromo-alpha,alpha-difluoroacetal can cyclize onto the olefinic part regiospecifically to give gamma-lactols in good yield. The lactols are then converted to the corresponding alpha,alpha-difluoro-gamma-lactones. Systematic synthesis of multifluorinated-alpha,alpha-difluoro-gamma-lactones has thus been accomplished through intramolecular radical cyclization as a key reaction. Semiempirical MO calculation study suggested a unique nature of alpha,alpha-difluoroacetate in that complete delocalization of the electrons in the SOMO orbital of alpha,alpha-difluoroacetyl radical occurred; this caused unsuccessful cyclization. To apply the present radical reaction, the first synthesis of both enantiomers of difluoroeldanolide, analogues of the sex pheromone of the male African sugarcane borer, has been demonstrated. Electrophysiological tests revealed that the difluorinated analogues were as active as the natural eldanolide on the olfactory receptors.