Triterpenoids from Ganoderma gibbosum: A Class of Sensitizers of FLC-Resistant Candida albicans to Fluconazole

Fungal drug resistance is a major health threat, and reports of clinical resistance worldwide are becoming increasingly common. In a research program to discover new molecules to help overcome this problem, 14 new lanostane-type triterpenoids, gibbosicolids A–G (2–8) and gibbosic acids I–O (9–15), were isolated from the fruiting bodies of Ganoderma gibbosum, along with seven known triterpenoid derivatives. These compounds featured high levels of oxidation, epimerization, and γ-lactonization. Structures were elucidated by comprehensive spectroscopic analyses and HRMS data. Absolute configurations were assigned based on quantum chemical calculations, including calculated chemical shift with DP4+ analysis, coupling constants, and electronic circular dichroism (ECD) methods. Results show that the calculated NMR with DP4+ analysis could not reliably establish the overall spatial configuration of molecules possessing independent and free-rotational stereoclusters. All these compounds significantly increased the sensitivity of fluconazole (FLC)-resistant C. albicans to FLC. Compounds 2, 5, 9, 12, 16, 17, and 21 exhibited strong antifungal activity against FLC-resistant C. albicans when combined with FLC, with MIC₅₀ values ranging from 3.8 to 8.8 μg/mL.