Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part I: Dihydronepetalactones

Chemical Composition and Anti-Candida Activity of Mentha suaveolens Ehrh. Essential Oils Obtained by Different Distillation Processes

A comparative study on essential oils extracted from Mentha suaveolens Ehrh. from Italy is reported. Two extraction procedures were investigated: hydrodistillation and steam distillation, carried out as a continuous and fractionated procedure. Fresh and dried plant material from two harvests was used. The hydrodistillation method yielded a higher amount of essential oil. The dried plant was significantly richer in essential oil per kg of starting plant material. Gas chromatography-mass spectrometry analysis of 112 samples showed that the essential oils belong to the piperitenone oxide-rich chemotype. In addition, piperitenone, p-cymen-8-ol, and limonene were among the most abundant compounds in the different samples. A higher amount of piperitenone oxide was obtained by hydrodistillation, while steam distillation gave a higher percentage of piperitenone and limonene. The essential oils were characterized for their anti-Candida albicans activity; higher potency was observed for the samples rich in piperitenone oxide, with MIC values ranging from 0.39 to 0.78 mg·mL-1 (0.039% and 0.078% p/v). The results of this work provide a deep insight into the methodology of essential oil extraction and the associated chemical variability of M. suaveolens Ehrh. Some of the essential oils are potent against C. albicans and could be considered for potential use in therapy.

Synthesis of Non-natural Aza-Iridoids via Ynamides and Molecular Networking-Based Tracing of Their In Planta Bioconversion

A synthesis of new-to-nature aza-iridoids via ynamides is presented. ZrCl₄ proved to be the best acid to perform this transformation. Various ynamides were accommodated, and seco-iridoids could be obtained as well. Aza-iridoids were infiltrated into leaves of Scrophularia Nodosa, an iridoid-producing plant species. High-resolution mass spectrometry coupled to computational metabolomic approaches was employed for the detection of aza-iridoid bioconversion products.

Mate attraction, chemical defense, and competition avoidance in the parasitoid wasp Leptopilina pacifica

A major hypothesis for the evolution of chemical signals is that pheromones arise from non-communicative precursor compounds. However, data supporting this hypothesis are rare, primarily because the original functions of the antecedent compounds often have been lost. A notable exception, however, is the parasitoid wasp species Leptopilina heterotoma, whose compound (−)-iridomyrmecin is used as a defensive secretion, a cue for females to avoid competition with con- and hetero-specific females, and as the primary component of the females’ sex pheromone. To better understand the evolution of sex pheromones from defensive compounds, we examined the chemical ecology of L. pacifica, the sister species of L. heterotoma. Here, we show that L. pacifica also produces a defensive secretion containing a species-specific mixture of mostly iridoid compounds. However, the composition of the secretion is more complex than in L. heterotoma, and iridomyrmecin is only a minor component. Moreover, in contrast to L. heterotoma, conspecific female competitors were not avoided by female subjects, and a role of the iridoids in the female sex pheromone of L. pacifica can be excluded, as only the females’ cuticular hydrocarbons (CHCs) resulted in the elicitation of courtship by males. Although closely related, the two sister species show substantial differences in the use of the defensive secretion for communicative purposes. Variation in pheromone usage in this genus still presents a conundrum, highlighting the need for additional studies to understand the selective forces shaping the evolution of pheromone composition.

Identification of the Cat Attractants Isodihydronepetalactone and Isoiridomyrmecin from Acalypha indica

Acalypha indica is a herb that grows throughout the tropical regions of the world. As well as being exploited for medicinal use, the roots of this plant are known to elicit a drug-like effect in cats. Recent research into feral cat control on Christmas Island has investigated whether a preparation of the roots of A. indica might be effective in traps to attract feral cats. However, the volatile nature of the attractants made it unviable for use in traps for more than a few days. In this study, we investigated the volatile components emitted by the plant roots and identified two iridoid compounds, (4R,4aR,7S,7aR)-isodihydronepetalactone and (4R,4aS,7S,7aR)-isoiridomyrmecin, which are known to affect behavioural activity in cats. Synthesis of standards confirmed the stereochemistry of both compounds emitted by the plant. Potential application of these compounds in feral cat control is discussed.

A general approach to iridoids by applying a new Julia olefination and a tandem anion-radical-carbocation crossover reaction

An efficient asymmetric approach to dihydronepetalactone and dolicholactone is presented featuring a Julia olefination and an anion–radical–cation crossover reaction.

The use of the lactone motif in chemical communication

A wide variety of organisms communicate via the chemical channel using small molecules. A structural feature quite often found is the lactone motif. In the present paper, the current knowledge on such lactones will be described, concentrating on the structure, chemistry, function, biosynthesis and synthesis of these compounds. Lactone semiochemicals from insects, vertebrates and bacteria, which this article will focus on, are particularly well investigated. In addition, some ideas on the advantageous use of lactones as volatile signals, which promoted their evolutionary development, will be discussed.

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part II: Iridomyrmecins

Following our earlier approach to the synthesis of dihydronepetalactones, all eight stereoisomers of trans-fused iridomyrmecins were synthesized starting from the enantiomers of limonene. Combined gas chromatography and mass spectrometry including enantioselective gas chromatography revealed that volatiles released by the endohyperparasitoid wasp Alloxysta victrix contain (4S,4aR,7S,7aR)-iridomyrmecin of 95–97% ee and stereochemically pure (4S,4aS,7R,7aS)-iridomyrmecin as a minor component.