Allobetulone rearrangement to l8αH,19βH-ursane triterpenoids with antiviral activity

Allobetulone E-ring rearrangement under treating with HClO₄ in Ac₂O under reflux afforded new triterpenoids: 3,28-diacetoxy-21-acetyl-2(3),20(21)-18α,19βH-ursandiene 3 and 3,28-diacetoxy-2(3),18(19)-oleandiene 4. 18α,19βH-Ursanes were transformed at A- and E-rings into indolo- and bis-furfurylidene 7 derivatives. Structure elucidation was performed using COSY, NOESY, HSQC and HMBC experiments, and X-Ray analysis for 3. The potential of newly obtained 18α,19βH-ursanes was evaluated against HCMV and HPV-11, the NCI-60 cancer cell panel and inhibition of α-glucosidase. All of the compounds have shown viral inhibition towards HCMV compared to standard drug Acyclovir. 3β-Acetoxy-21β-acetyl-20β,28-epoxy-18α,19βН-ursane 1 showed moderate activity (EC₅₀ 4.87 μM) towards the HCMV-resistant isolate (GDGr K17) compared to standard drug Cidofovir and was four times more potent than Ganciclovir. Compound 7 inhibited the cell growth of the three melanoma and one colon cancer cell. 3-Oxo-21β-acetyl-20β,28-epoxy-18α,19βН-ursane 5 and compound 7 inhibited α-glucosidase with IC₅₀ 28.0 µM and 4.0 µM being from 6 to 44 times more active than acarbose.