HSQC-guided discovery and structural optimization of antiadipogenic indole diterpenoids from endophytic fungus Penicillium janthinellum H-6.

Chemical investigation of Penicillium janthinellum H-6 using HSQC-guided small molecule accurate recognition technology (SMART) led to the isolation of nine new indole diterpenoids (IDTs), penijanidines D-L (1-9), along with four known analogues (10-13). Architecturally, compound 1 represents an unusual imine-containing IDT, while compounds 2 and 3 are rare 1(2),2(18)-di-seco-IDT derivatives. Their structures including absolute configuration were determined by spectroscopic analysis and computational method. Meanwhile, structure optimization of the primary penijbirine (15) was conducted to obtain 22 new IDT derivatives (21-42). Systematic evaluation of the antiadipogenic effects of 42 IDTs, including 13 isolated ones (1-13), seven previously reported ones (14-20), and 22 semi-synthetic derivatives (21-42), in 3T3-L1 adipocytes identified the structurally optimized derivative 38 as the most potent molecular for triglyceride-lowering activity, exhibiting an EC50 value of 0.25 ± 0.05 μM. Preliminary structure-activity relationship (SAR) analysis highlighted critical pharmacophoric features governing the lipid-lowering efficacy of these compounds. Mechanism studies revealed that 38 suppressed adipogenesis and lipogenesis via activating the AMPK signaling pathway, evidenced by significantly increased phosphorylation of AMPK (p-AMPK). Surface plasmon resonance (SPR) assays further confirmed that compound 38 directly bond to the AMPK protein with an affinity of KD = 12.4 μM. This study not only expands the chemical diversity of bioactive IDTs but also identifies 38 as a novel AMPK-targeting lead compound for potential anti-obesity drug development.