Tandyukisins K–P, New Decalin Polyketides from Trichoderma longicollum 17007 with Antitubercular Activity Against Mycobacterium tuberculosis H37Ra

Background: Endophytic fungi are important sources of structurally diverse antimicrobial natural products, but their potential to yield antitubercular scaffolds remains insufficiently explored. This study aimed to uncover new decalin polyketides from the endophytic fungus, Trichoderma longicollum 17007, and to evaluate their biological activity. Methods: Feature-based molecular networking (FBMN) analysis of the ethyl acetate extract from rice-based cultures was performed using trichoharzin as a seed compound to guide targeted isolation. Structures were established by HRMS, 1D and 2D NMR spectroscopy, NOESY analysis, and quantum chemical ECD calculations. Cytotoxicity and activity against the avirulent Mycobacterium tuberculosis H37Ra strain were evaluated, and genome mining was performed to identify a candidate biosynthetic gene cluster. Results: Six new decalin polyketides, tandyukisins K–P (1–6), and two known analogues, trichoharzin (7) and tandyukisin J (8), were isolated. Compounds 1–6 are C1-O-acetylated analogues bearing a 3-methylpentenedioate-type acyl side chain. Comparative 13C NMR analysis revealed empirical features useful for assigning side-chain attachment site, double-bond position and geometry. Tandyukisins K (1) and P (6) showed moderate activity against the avirulent M. tuberculosis H37Ra strain, with a MIC value of 12.5 μg/mL. Conclusions: These findings expand the structural diversity of decalin polyketides and provide the first evidence of antitubercular activity by this compound family.