Phenylacetonitrile acts as an aposematic signal and toxin precursor against predation in locusts.

Chemical communication plays an important role in density-dependent phase change in locusts. However, the volatile components and emission patterns of the migratory locust, Locusta migratoria, are largely unknown. In this study, we identified the chemical compositions and emission dynamics of locust volatiles from the body and feces and associated them with developmental stages, sexes and phase changes. The migratory locust shares a number of volatile components with the desert locust (Schistocerca gregaria), but the emission dynamics of the two locust species are significantly different. The body odors of the gregarious nymphs in the migratory locust consisted of phenylacetonitrile (PAN), benzaldehyde, guaiacol, phenol, aliphatic acids and 2,3-butanediol, and PAN was the dominant volatile. Volatiles from the fecal pellets of the nymphs primarily consist of guaiacol and phenol. Principal component analysis (PCA) showed significant differences in the volatile profiles between gregarious and solitary locusts. PAN and 4-vinylanisole concentrations were significantly higher in gregarious individuals than in solitary locusts. Gregarious mature males released significantly higher amounts of PAN and 4-vinylanisole during adulthood than mature females and immature adults of both sexes. Furthermore, PAN and 4-vinylanisole were completely lost in gregarious nymphs during the solitarization process, but were obtained by solitary nymphs during gregarization. The amounts of benzaldehyde, guaiacol and phenol only unidirectionally decreased from solitary to crowded treatment. Aliphatic aldehydes (C7 to C10), which were previously reported as locust volatiles, are now identified as environmental contaminants. Therefore, our results illustrate the precise odor profiles of migratory locusts during developmental stages, sexes and phase change. However, the function and role of PAN and other aromatic compounds during phase transition need further investigation.

Asiaticoside (1), namely,2 a,3b,23-trihydroxy-urs-12-en-28-oic-O-a-l-rhamnopyranosyl-(1!4)-b-d-glucopyranosyl-(1!6)-b-d-glucopyranoside,t he major activeb iomarker of the traditional medicinal plant Centella asiatica,h as been synthesized for the first time. The strategy features alate-stage gold(I)-catalyzed glycosidic condensation of atriterpenoid acid and at risaccharide ortho-hexynylbenzoate. The overall preparation required at otal 31 steps with the longest linear sequence occurring over 14 steps in a6 % overall yield and startingf rom ursolic acid (3b-hydroxy-urs-12-en-28-oic acid). IntroductionCentella asiatica (L.) Urban, the synonym of which is Hydrocotyle asiatica L. and also knowna sg otu kola or Indianp ennywort, grows widely in tropical regions. It hasb een used since prehistoric times as ac ure-all, but most prominently it has been used fort he treatmento fd ermatoses and skin lesions such as excoriations, burns, and hypertrophic scars.[1] The major active biomarker of C. asiatica hasb een identified as an ursane-type triterpene glycoside, namely,a siaticoside (1). [2] Indeed, it has been reported that asiaticoside can stimulate collagen synthesis, [3] possibly through activation of the Smad pathway [3a] or the inhibition of glycogen phosphorylase.[4a] Asiaticoside( 1)i so ne of the earliestc haracterized saponins, [2a] and its structure was unambiguously established in 1987 by Xray diffraction as 2a,3b,23-trihydroxy-urs-12-en-28-[2b] Although analogues,m ostly derivatized from the aglycone,h ave been synthesized for structureactivity relationship studies, [4] the total synthesis of asiaticoside has not been realized.I nl ine with our prolonged interest in the chemical synthesis of saponins for biological studies, [5] we embarked on the preparation of asiaticoside( 1), and we herein reporti ts first total synthesis. Results and DiscussionAsiaticoside (1)c onsists of 2a,3b,23-trihydroxy-urs-12-en-28-oic acid (i.e.,a siatic acid) as an aglycone with ag lycan moiety attached at the ester linkage at C28. The convergent synthesis calls for the condensation of an asiatic acid derivativewith atrisaccharide donor, [5] such as the condensation between 3 and 2 ( Figure 1). Fortunately,t he linear trisaccharide allows for the installation of ap articipating group (i.e.,abenzoyl group) at C2 of the first glucose unit to ensure the required b-selective glycosylation.I nl ine with our current practice regarding gold(I)-catalyzed glycosylations with glycosyl ortho-alkynylbenzoates as donors, [6] perbenzoyl trisaccharide n-hexynylbenzoate 2 was envisioned asareliable donor.A siatic acid derivative 3 could be synthesized from commerciallya vailableu rsolic acid (4), throught he introduction of the 23-and 2a-hydroxy groups. [7] Given the robustness of the triterpenoid 28-ester linkage, we employed acetyl and benzoyl groups as permanent protecting groups,w hich couldb eg lobally removed without the hydrolysis of this typical triterpene glycosidic linkage. [5] We commencedt he synthesis by ...