Dahurelmusin A, a Hybrid Peptide–Polyketide from Elymus dahuricus Infected by the Epichloë bromicola Endophyte

Antifungal, repellency, and insecticidal activities of Cymbopogon distans and Ruta graveolens essential oils and their main chemical constituents

Essential oils produced by Cymbopogon distans and Ruta graveolens with a similar Chinese name could be explained as book fragrance in the Chinese idiom, "shu xiang men di", namely, a wealthy intellectual family according to ancient Chinese. Therefore , volatile oils from these two plants and their main compounds were tested to explore their antifungal, repellent and insecticide actions. In this study, essential olis (EOs) of C. distans exhibited significant antifungal activity against Rhizopus stolonifera ( 97%), Mucor racemosus (97%), and Trichoderma viride (84%); its main compounds display interesting activity, such as methyleugenol (87%) and elemicine (85%) against T. viride , and butyl hydroxytoluene against M. racemosus (90%) and R. stolonifera (95%). EOs of R. graveolens and other major chemical constituents showed weak inhibitory effects against other fungi ( Aspergillus flavus and Fusarium oxysporum ). Then, EOs ( C. distans and R. graveolens ) and its main compounds exhibited obvious repellent activity (more than 85%) at the concentration of 16 nL/cm², which was consistent with the repellency of the positive control (DEET). In terms of insecticidal activity, the mortality of C. distans volatile oil against R. padi (56.4%) was lower than that of R. graveolens volatile oil (92.4%), and all compounds showed strong lethal effects. These results provide a natural substance for controlling fungi and insects when storing books, and which can be used as a biological pesticide for industrial production. Through our study, the book fragrance in the Chinese idiom "shu xiang men di" was speculated to be the EO odor of C. distans.

Epichloë Fungal Endophytes-From a Biological Curiosity in Wild Grasses to an Essential Component of Resilient High Performing Ryegrass and Fescue Pastures

The relationship between Epichloë endophytes found in a wide range of temperate grasses spans the continuum from antagonistic to mutualistic. The diversity of asexual mutualistic types can be characterised by the types of alkaloids they produce in planta. Some of these are responsible for detrimental health and welfare issues of ruminants when consumed, while others protect the host plant from insect pests and pathogens. In many temperate regions they are an essential component of high producing resilient tall fescue and ryegrass swards. This obligate mutualism between fungus and host is a seed-borne technology that has resulted in several commercial products being used with high uptake rates by end-user farmers, particularly in New Zealand and to a lesser extent Australia and USA. However, this has not happened by chance. It has been reliant on multi-disciplinary research teams undertaking excellent science to understand the taxonomic relationships of these endophytes, their life cycle, symbiosis regulation at both the cellular and molecular level, and the impact of secondary metabolites, including an understanding of their mammalian toxicity and bioactivity against insects and pathogens. Additionally, agronomic trials and seed biology studies of these microbes have all contributed to the delivery of robust and efficacious products. The supply chain from science, through seed companies and retailers to the end-user farmer needs to be well resourced providing convincing information on the efficacy and ensuring effective quality control to result in a strong uptake of these Epichloë endophyte technologies in pastoral agriculture.

Do Epichloë Endophytes and Their Grass Symbiosis Only Produce Toxic Alkaloids to Insects and Livestock?

Epichloë endophytes in forage grasses have attracted widespread attention and interest of chemistry researchers as a result of the various unique chemical structures and interesting biological activities of their secondary metabolites. This review describes the diversity of unique chemical structures of taxa from Epichloë endophytes and grass infected with Epichloë endophytes and demonstrates their reported biological activities. Until now, nearly 160 secondary metabolites (alkaloids, peptides, indole derivatives, pyrimidines, sesquiterpenoids, flavonoids, phenol and phenolic acid derivatives, aliphatic metabolites, sterols, amines and amides, and others) have been reported from Epichloë endophytes and grass infected with Epichloë endophytes. Among these, non-alkaloids account for half of the population of total metabolites, indicating that they also play an important role in Epichloë endophytes and grass infected with Epichloë endophytes. Also, a diverse array of secondary metabolites isolated from Epichloë endophytes and symbionts is a rich source for developing new pesticides and drugs. Bioassays disclose that, in addition to toxic alkaloids, the other metabolites isolated from Epichloë endophytes and symbionts have notable biological activities, such as antifungal, anti-insect, and phytotoxic activities. Accordingly, the biological functions of non-alkaloids should not be neglected in the future investigation of Epichloë endophytes and symbionts.

Total Synthesis and Stereochemical Revision of Stereocalpin A: Mirror-Image Approach for Stereochemical Assignments of the Peptide-Polyketide Macrocycle

Stereocalpin A is a cyclic depsipeptide with cytotoxic activity isolated from the Antarctic lichen Stereocaulon alpinum. Although a number of synthetic investigations of the unprecedented 12-membered macrocycle of stereocalpin A with a dipeptide segment and a polyketide substructure have been conducted, the configurational assignment has not been completed. In this study, we achieved the first total synthesis and stereochemical revision of stereocalpin A. To facilitate the comprehensive assessment of eight possible stereocalpin A isomers, four stereoisomers of polyketide precursors were conjugated with l-Phe-l-MePhe and d-Phe-d-MePhe dipeptides (MePhe: N-methylphenylalanine) to provide four possible isomers and four mirror-image structures of the remaining isomers, respectively. The comparative NMR analysis of a series of stereoisomers revealed that stereocalpin A possesses 2 R,4 S,5 R-configurations, which is unique among the related 12-membered hybrid peptide-polyketide natural products reported recently. The NOE correlations in the polyketide substructure of stereocalpin A were also retrospectively analyzed among the eight possible stereoisomers.

Hot off the press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as furanmonogone A from Hypericum monogynum.