Dienic analogs of (Z)-5-decenyl acetate, a pheromone component of the turnip moth, Agrotis segetum: Synthesis, conformational analysis and structure-activity relationships

Characterizing human odorant signals: insights from insect semiochemistry and in silico modelling

Interactions relating to human chemical signalling, although widely acknowledged, are relatively poorly characterized chemically, except for human axillary odour. However, the extensive chemical ecology of insects, involving countless pheromone and other semiochemical identifications, may offer insights into overcoming problems of characterizing human-derived semiochemicals more widely. Current techniques for acquiring insect semiochemicals are discussed, particularly in relation to the need for samples to relate, as closely as possible, to the ecological situation in which they are naturally deployed. Analysis is facilitated by chromatography coupled to electrophysiological preparations from the olfactory organs of insects in vivo. This is not feasible with human olfaction, but there are now potential approaches using molecular genetically reconstructed olfactory preparations already in use with insect systems. There are specific insights of value for characterizing human semiochemicals from advanced studies on semiochemicals of haematophagous insects, which include those involving human hosts, in addition to wider studies on farm and companion animals. The characterization of the precise molecular properties recognized in olfaction could lead to new advances in analogue design and a range of novel semiochemicals for human benefit. There are insights from successful synthetic biology studies on insect semiochemicals using novel biosynthetic precursors. Already, wider opportunities in olfaction emerging from in silico studies, involving a range of theoretical and computational approaches to molecular design and understanding olfactory systems at the molecular level, are showing promise for studying human semiochemistry. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

The Augmenting Effects of Desolvation and Conformational Energy Terms on the Predictions of Docking Programs against mPGES-1

In this study we introduce a rescoring method to improve the accuracy of docking programs against mPGES-1. The rescoring method developed is a result of extensive computational study in which different scoring functions and molecular descriptors were combined to develop consensus and rescoring methods. 127 mPGES-1 inhibitors were collected from literature and were segregated into training and external test sets. Docking of the 27 training set compounds was carried out using default settings in AutoDock Vina, AutoDock, DOCK6 and GOLD programs. The programs showed low to moderate correlation with the experimental activities. In order to introduce the contributions of desolvation penalty and conformation energy of the inhibitors various molecular descriptors were calculated. Later, rescoring method was developed as empirical sum of normalised values of docking scores, LogP and Nrotb. The results clearly indicated that LogP and Nrotb recuperate the predictions of these docking programs. Further the efficiency of the rescoring method was validated using 100 test set compounds. The accurate prediction of binding affinities for analogues of the same compounds is a major challenge for many of the existing docking programs; in the present study the high correlation obtained for experimental and predicted pIC₅₀ values for the test set compounds validates the efficiency of the scoring method.

Structure-activity relationships for chain-shortened analogs of (Z)-5-decenyl acetate, a pheromone component of the turnip moth,Agrotis segetum

Structure-activity relationships for chain-shortened analogs of (Z)-5-decenyl acetate, a pheromone component of the turnip moth,Agrotis segetum, have been studied by electrophysiological single-sensillum technique and interpreted in terms of a previously reported receptor-interaction model. The results indicate that the terminal methyl group, as well as the acetate group, interacts with highly complementary receptor sites. The terminal alkyl chain is suggested to interact with a hydrophobic "pocket" extending over the two methylene groups closest to the terminal methyl group. The amounts of stimulus actually released from the odor source have been studied. The results demonstrate the necessity to take differences of volatility into account in comparisons of electrophysiological data for compounds of different chain lengths. It is shown that relative vapor pressures may to a good approximation be employed to estimate correction factors.

Introduction of methyl groups to acetate substituted chain of (Z)-5-decenyl acetate, a pheromone component of turnip moth,agrotis segetum: synthesis, single-sensillum recordings, and structure-activity relationships

Methyl-substituted analogs of (Z)-5-decenyl acetate, a pheromone component of the turnip moth,Agrotis segetum, have been synthesized and studied by electrophysiological single-sensillum recordings and molecular mechanics calculations [MM2(85)]. The analogs are monomethyl substituted in the 2, 3, 4, and 5 positions and geminally dimethyl substituted in the 2, 3, and 4 positions. The methyl groups have been employed as space probes to study the degree of steric complementarity between the acetate-substituted alkyl chain of the pheromone component and its receptor. The electrophysiological activities, interpreted in terms of a receptor interaction model, indicate significant steric repulsive interactions between the introduced methyl groups and the receptor. This implies a high degree of complementarity between the acetate-substituted alkyl chain of the natural pheromone component and its receptor.

Behavioral and electrophysiological activity of (Z,E)-7,9,11-dodecatrienyl formate, a mimic of the major sex pheromone component of carob moth,Ectomyelois ceratoniae

The behavioral and electrophysiological activity of a mimic [(Z,E)7,9,11-dodecatrienyl formate] of the major sex pheromone component [(Z,E) 9,11,13-tetradecatrienal] of carob moth was assessed. Wind-tunnel bioassays demonstrated that the formate was as effective as natural gland extracts, and significantly more effective than the trienal alone or than the trienal blended with two minor pheromone components, in evoking source contact. Dispensers containing the formate were as effective as trienal-containing blend lures in attracting males when placed at the same dosage in traps in date gardens. Single-cell recordings showed that at least two olfactory neurons, differentiated by spike amplitude, are located in the long trichoid hairs on male carob moth antennae. Dose-response relationships indicated that puffs from cartridges loaded with at least 0.1 μg of the formate or of the trienal were necessary to elicit spiking by either the small or the large-spiking cell within a sensillum. Cross-adaptation studies demonstrated that both compounds stimulated the same large-spiking cell. The frequencies of spikes evoked from the large cell when stimulated by emissions from 0.1-μg, 1-μg, or 10-μg cartridges of either the formate or the trienal were not significantly different, suggesting that the formate is an effective mimic of the trienal at the antennal receptor cell level.

Enantiomers of methyl substituted analogs of (Z)-5-decenyl acetate as probes for the chirality and complementarity of its receptor inAgrotis segetum 1: Synthesis and structure-activity relationships

The enantiomers of analogs of (Z)-5-decenyl acetate, a pheromone component ofAgrotis segetum, substituted by a methyl group in the 2, 3, 4, 7, and 8 positions and dimethyl substituted in the 4,7 positions, have been synthesized and studied by an electrophysiological single-cell technique and by molecular mechanics calculations. The results demonstrate that the electrophysiological activity as well as the ability of the (Z)-5-decenyl acetate receptor to differentiate between enantiomers depends on the position of the methyl substituent. For analogs methyl substituted in the 2, 4, or 8 position, no differences in the activities of the enantiomers could be observed. In contrast, the enantiomers of the 3- and 7-methyl analogs display a significant difference in the activities, theR-enantiomers being more active than theS-enantiomers. From an analysis of the structure-activity results of the enantiomers of the 4,7-dimethyl-substituted analogs, the chiral sense of the alkylchain of the natural pheromone component on binding to its receptor could be deduced.

Synthesis and biological activity of conformationally restricted gypsy moth pheromone mimics

The design and synthesis of a series of conformationally constrained mimics of gypsy moth sex pheromone, (+)-disparlure (7R,8S)-2-methyl-7,8-epoxyoctadecane, are described. The core structure of the mimics is derived from 5-(2'-hydroxyethyl)cyclopent-2-en-1-ol. Substituent optimization of the analogs was accomplished through the synthesis of mini-libraries and pure individual compounds, followed by electrophysiological experiments with male gypsy moth antennae. The electroantennogram results show that the analogs elicited weak to no antennal responses themselves. There was a clear structure-activity pattern for odorant activity, with ethyl substituents being best. Further, when puffed simultaneously with the pheromone, some of the compounds gave a significant enhancement of the antennal depolarization, indicating an additive or synergistic effect. A pure pheromone stimulus following a mixed compound/pheromone stimulus was generally not affected, with two exceptions: one compound enhanced and another inhibited a subsequent stimulus. The compounds also prolonged the stimulation of the antenna, which manifested itself in widened electroantennogram peaks. We tested the hypothesis that this prolonged stimulation may be due to the stabilization of a particular conformer of the pheromone-binding protein (PBP). Compounds that caused PBP2 to adopt a similar conformation than in the presence of pheromone also caused peak widening. This was not the case with PBP1.

Insect parapheromones in olfaction research and semiochemical-based pest control strategies

The possibility of disrupting the chemical communication of insect pests has initiated the development of new semiochemicals, parapheromones, which are anthropogenic compounds structurally related to natural pheromone components. Modification at the chain and/or at the polar group, isosteric replacements, halogenation or introduction of labeled atoms have been the most common modifications of the pheromone structure. Parapheromones have shown a large variety of effects, and accordingly have been called agonists, pheromone mimics, synergists and hyperagonists, or else pheromone antagonists, antipheromones and inhibitors. Pheromone analogues have been used in quantitative structure-activity relationship studies of insect olfaction, and from a practical point of view they can replace pheromones when these are costly to prepare or unstable under field conditions.

Enantiomers of cis- and trans-3-(4-propyl-cyclopent-2-enyl) propyl acetate. A study on the bioactive conformation and chiral recognition of a moth sex pheromone component

The enantiomers of cis- and trans-3-(4-propyl-cyclopent-2-enyl) propyl acetate, which are conformationally constrained analogues of (Z)-5-decenyl acetate (1), a sex pheromone component of the turnip moth, Agrotis segetum, have been synthesized and tested using the electrophysiological single-sensillum technique. The analogues mimic a cisoid and transoid conformation of 1, respectively. In addition, the enantiomers of each of the cis- and trans-isomers are conformationally constrained analogues of enantiomeric cisoid and transoid conformations of 1. Thus, the compounds prepared and tested are well suited to investigate the nature of the bioactive conformation of the natural pheromone component 1 and the chiral sense of its interaction with the receptor. Electrophysiological single-sensillum recordings show that the activity of the most active cis-isomer, which has a (1S,4R)-configuration, is more than two orders of magnitude higher than that of the most active trans-isomer. Furthermore, the (1S,4R)-isomer is at least 100 times more active than its enantiomer. These results strongly support a previously proposed cisoid bioactive conformation of 1. Furthermore, the (1S,4R)-configuration of most active stereoisomer identifies the chiral sense of the interaction between the natural pheromone component 1 and its receptor.

Ab initio calculations on (Z)-5-decenyl acetate, a component of the pheromone complex of Agrotis segetum (Lepidoptera: Noctuidae) and electrophysiological studies with chain elongated analogues

Conformational analyses of (Z)-5-decenylacetate, a sex pheromone component of the turnip moth, Agrotis segetum, and double unsaturated pheromone analogues 4 and 5 have been performed by ab initio calculations using Gaussian 92. Two minima were found for a cisoid and a transoid conformer, differing for 0.03 kcal/mol only. Conformational energies of diene analogues (5Z,7E)-5,7-decadienyl acetate (4) and (3E,5Z)-3,5,-decadienyl acetate (5) were determined for conformers required to mimic spatial relationships of the cisoid conformation of the natural pheromone 2. Finally, single sensillum recording studies were carried out with chain elongated C11- to C16-pheromone analogues 6.

Conformationally constrained analogues of (Z)-5-decenyl acetate, a pheromone component of Agrotis segetum

Conformationally constrained analogues of (Z)-5-decenyl acetate (1), a pheromone component of the turnip moth, Agrotis segetum, have been synthesized and tested by using electrophysiological single-cell recordings. In the constrained analogues the terminal alkyl chain in 1 has been incorporated in a six-membered (3 and 4) or five-membered (6) ring system. These cycli compounds are also conformationally constrained analogues of the previously deduced bioactive conformations of the corresponding chain-elongated analogues 2 and 5. The electrophysiological activities of the constrained analogues are found to be significantly lower than that of the natural pheromone component 1, most probably due to steric repulsive interactions between the analogue and the receptor, and also lower than the activities of the corresponding chain-elongated analogues of 1. It is concluded that the flexibility of the terminal chains in 2 and 5 is essential for the possibility of the receptor to accommodate these parts of the chain-elongated analogues in their bioactive conformations.