Two New naphthalene-chroman coupled derivatives from the mangrove-derived fungus Cladosporium sp. JJM22

Highlights

• A bioactive secondary metabolites investigation of Cladosporium sp. JJM22 was carried out.

• Two new naphthalene-chroman coupling derivatives were isolated and characterized.

• Compounds 1 and 2 had a broad spectrum antibacterial or antifungal activity.

Abstract

Two new naphthalene-chroman coupling derivatives, cladonaphchroms A (1) and B (2), along with four known compounds (3-6) were obtained from EtOAc extract of the mangrove-derived fungus Cladosporium sp. JJM22. Their structures were elucidated by detailed analysis of comprehensive spectroscopic data. Compounds 1 and 2 exhibit antibacterial or antifungal activities.

Introduction

Endophytic fungi as rich sources of new biologically active natural products, more and more secondary metabolites were reported from endophytic fungi (Blunt et al., 2018; Carroll et al., 2019). Chemical investigations of mangrove-derived endophytic fungi, especially those from the subtropical island of Hainan, P. R. China, have shown a sharp increase in recent years (Liao et al., 2019; Zheng et al., 2018; Zhou et al., 2014). Among these secondary metabolites, many antibacterial and antifungal metabolites were reported such as thiocladospolide G, penixylarins C, (2S)-2,3-dihydro-5,6-dihydroxy-2-methyl-4H-1-benzopyran-4-one (I), 4-ethyl-3-hydroxy-6-propenyl-2H-pyran-2-one, 5-hydroxy-2,3-dihydroxymethyl-7- methoxychromone, bafilomycin K (He et al., 2020; Luo et al., 2019; Wang et al., 2020; Yu et al., 2019; Zhang et al., 2011). Our group recently reported the isolation of one new ribofuranose phenol derivative, 4-O-α-D-ribofuranose-3-hydroxymethyl- 2-pentylphenol and one new naphthalene derivative, (-)-trans-(3R,4R)-3,4,8- trihydroxy-6,7-dimethyl-3,4-dihydronaphthalen-1(2H)-one from the endophytic fungus Cladosporium sp. JJM22 in solid rice medium (Wu et al., 2019).

In order to search for significant bioactive natural products from the endophytic fungus Cladosporium sp. JJM22, the culture condition was changed to potato glucose liquid medium. The EtOAc extract of the fungal culture exhibited antibacterial activity. Bioassay guided fractionation of the EtOAc extract led to the isolation of two new naphthalene-chroman coupling derivatives, cladonaphchroms A (1) and B (2), along with four known compounds, (R)-5-hydroxy-2-methylchroman-4-one (3) (Zilla et al., 2013), 5-hydroxy-2-methyl-4H-chromen-4-one (4) (Dai et al., 2006), 1,8-dimethoxynaphthalene (5) (Dai et al., 2009), and 8-methoxynaphthalen-1-ol (6) (Dai et al., 2009) (Fig. 1). Herein, we report the isolation, structure elucidation and biological activities of these compounds.