Bipolenins K-N: New sesquiterpenoids from the fungal plant pathogen Bipolaris sorokiniana.

Chin-Soon Phan,Peter S Solomon,Yit-Heng Chooi,Hang Li,Andrew M Piggott,Simon Kessler

doi:10.3762/bjoc.15.198

Chin-Soon Phan, Peter S Solomon + Show 4 more

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https://doi.org/10.3762/bjoc.15.198

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Abstract

Chemical investigation of the barley and wheat fungal pathogen Bipolaris sorokiniana BRIP10943 yielded four new sativene-type sesquiterpenoid natural products, bipolenins K–N (1–4), together with seven related known analogues (5–11), and a sesterterpenoid (12). Their structures were determined by detailed analysis of spectroscopic data, supported by TDDFT calculations and comparison with previously reported analogues. These compounds were evaluated for their phytotoxic activity against wheat seedlings and wheat seed germination. The putative biosynthetic relationships between the isolated sesquiterpenoids were also explored.

Highlights

Fungi belonging to the genus Bipolaris have been reported to produce a diverse array of secondary metabolites, including sesquiterpenes [1,2,3,4,5,6,7], sesquiterpene-xanthones [8], diterpenes [9], sesterterpenes [10], cochlioquinones and peptides [11]
Following the first and only reported isolation of a sativenetype sesquiterpenoid, sorokinianin (11), from B. sorokiniana in 1994 [2], we have expanded the number of reported analogues to eleven
We demonstrated that 6 and 10 have weak necrotic activity against wheat leaves, while 7 inhibited wheat seed germination at 100 ppm

Summary

Introduction

Fungi belonging to the genus Bipolaris (teleomorph: Cochliobolus) have been reported to produce a diverse array of secondary metabolites, including sesquiterpenes [1,2,3,4,5,6,7], sesquiterpene-xanthones [8], diterpenes [9], sesterterpenes [10], cochlioquinones and peptides [11]. The 13C NMR spectrum (Figure S2, Supporting Information File 1) showed 15 distinct carbon signals, while 13C and 1H NMR data (Table 1) indicated an isopropyl unit (δC 28.3, 29.2 and 73.1; δH 1.20 and 1.24), one tertiary methyl (δC 20.1; δH 1.25), a disubstituted olefin (δC 105.7 and 155.2; δH 5.12 and 4.89) and four methines (δC 39.6, 51.1, 51.6 and 54.0; δH 1.73, 1.88, 2.65 and 3.77), which are typical resonances for sativene-type sesquiterpenoids.

Results

Conclusion