A New Meroditerpene and a New Tryptoquivaline Analog from the Algicolous Fungus Neosartorya takakii KUFC 7898

Abstract

A new meroditerpene sartorenol (1), a new natural product takakiamide (2) and a new tryptoquivaline analog (3) were isolated, together with nine known compounds, including aszonapyrone A, chevalone B, aszonalenin, acetylaszonalenin, 3'-(4-oxoquinazolin-3-yl) spiro[1H-indole-3,5'-oxolane]-2,2'-dione, tryptoquivalines L, F and H, and the isocoumarin derivative, 6-hydroxymellein, from the ethyl acetate extract of the culture of the algicolous fungus Neosartorya takakii KUFC 7898. The structures of the new compounds were established based on 1D and 2D NMR spectral analysis, and, in the case of sartorenol (1) and tryptoquivaline U (3), X-ray analysis was used to confirm their structures and to determine the absolute configuration of their stereogenic carbons. Compounds 1, 2 and 3 were evaluated for their antimicrobial activity against Gram-positive and Gram-negative bacteria, and multidrug-resistant isolates from the environment; however, none exhibited antibacterial activity (MIC ˃ 256 mg/mL). The three new compounds did not show any quorum sensing inhibition in the screening protocol based on the pigment production by Chromobacterium violaceum (ATCC 31532).

Keywords: 6-hydroxymellein; Neosartorya takakii; aszonalenin; aszonapyrone A; chevalone B; meroditerpene; sartorenol; tryptoquivaline U.

Figure 1

New secondary metabolites isolated from the ethyl acetate extract of the culture of N. takakii KUFC 7898.

Figure 2

Ortep view of sartorenol (1).

Figure 3

Proposed biogenesis of sartorenol (1).

Figure 4

Conformations of C-11R stereoisomer of compound 2 obtained by simulation performed with ChemBio3D Ultra 14.0; (a) conformer with H-11 in equatorial position; (b) conformer with H-11 in axial position.

Figure 5

Ortep view of tryptoquivaline U (3).