Paraconiothenes A-K: Bergamotane Sesquiterpenoids with Selective Antifungal Activities from Paraconiothyrium sp.

Eleven new bergamotane sesquiterpenoids, including seven unusual 6/4 bicyclic trinor-analogues (1-7), one 6/4/6 tricyclic trinor-analogue featuring a unique tetrahydro-2H-pyran-2-one residue (8), one rare 6/4/5/5 tetracyclic polyoxygenated trinor-analogue (9), and two tricyclic sesquiterpenoids with the [4.3.0.05,6] nonan (10) and [3.3.1.05,6] nonan (11), were isolated from endophytic Paraconiothyrium sp. YHH-11. The structures were identified by NMR, HRESIMS, DP4+ analysis, and ECD calculations, and a plausible biosynthetic pathway was proposed. Pathogenicity assays showed that only Paraconiothyrium archidendri YHP-1 caused chlorosis, browning, and necrosis symptoms on detached leaves of Cerasus serrulata, Brassica chinensis L., and Brassica oleracea L. Compounds 1-3, 5-8, and 10 exhibited significant antifungal activities against at least one tested strain, comparable to nystatin (1 μg/mL). Notably, compounds 2 and 5 selectively inhibited P. archidendri YHP-1, with MICs of 1 μg/mL. Compound 2 further exhibited concentration-dependent protective efficacy on detached C. serrulata leaves, highlighting its potential as a selective antifungal candidate.