Seamounts are generally the uplifted terrain on the seafloor above 1000 m with a limited area across the summit that appear as a conical shape with a circular, elliptical, or more elongated base [1], [2]. The Magellan Seamounts are located in the Western Pacific Ocean, which are characterized by unique ecosystems and abundant biodiversity due to the specific geographical and hydrological conditions [3], [4], [5]. Microbes inhabiting the deep-sea seamounts could produce diverse secondary metabolites with distinctive structures to confer a survival advantage in the unique environment. In our previous research, chemical investigations were performed on an endozoic fungus Talaromyces scorteus AS-242, isolated from the fresh inner tissue of the deep-sea anemone Cerianthus sp. that was collected from the Magellan Seamounts. Eight new diterpenoid acids possessing potent antimicrobial activity were isolated and identified from the fungus T. scorteus AS-242 when cultured in the potato-dextrose broth [6]. Subsequently, the fungus T. scorteus AS-242 was fermented in the solid rice medium, which resulted in characterizations of three new antimicrobial polyketide derivatives including two nonadrides and one depsidone from the less polar extraction of the culture [7].

As part of our ongoing effort to uncover secondary metabolites with intriguing structures and significant biological activities [8], [9], further isolation and identification were performed on the remaining fractions of the fungal culture in the solid rice medium. As a result, seven new secondary metabolites with four different structural classes (Fig. 1), including two cycloheptapeptides (1 and 2), two 19-nor-diterpenoids (3 and 4), two diterpenoid acids (5 and 6), and one triterpenoid (7) were characterized. The structures and absolute configurations of compounds 1−7 were comprehensively assigned by spectroscopic data analysis, single-crystal X-ray diffraction, tandem mass spectrometry, as well as electronic circular dichroism (ECD) calculations. This paper describes the details of the isolation, structure elucidation, and antimicrobial evaluation of compounds 1−7.