Swiemagalins A-C: three new phragmalins from the stem barks of Indonesian Swietenia mahagoni and cytotoxic activities

This study aimed to isolate three new phragmalin-type limonoids, swiemagalins A–C (1–3), as well as two known limonoids (4 and 5) from the stem barks of Indonesian Swietenia mahagoni. Compounds 1–3 were classified as highly oxygenated phragmalin-type limonoids, with 1 featuring an opened D-ring and bulky substituents, while 2 and 3 possessed a seco-δ-lactone moiety and a biosynthetically unique C–C connectivity in D-ring. The planar structures and absolute configurations were determined through a combination of extensive spectroscopic methods. These included High-Resolution Electrospray Ionisation Mass Spectrometry (HR-ESI-MS), Infra-red (IR) spectroscopy, comprehensive Nuclear Magnetic Resonance (NMR) analyses, Electronic Circular Dichroism (ECD), and quantum chemical calculations using Time-Dependent Density Functional Theory (TD-DFT). Cytotoxic activity of 1–5 was evaluated against human breast cancer (MCF-7) and normal kidney (CV-1) cell lines.