# Calabanones A‒H, chromanone derivatives from the stem bark of Calophyllum calaba and their cytotoxic activities against cancer cells

## TL;DR

Researchers discovered eight new chromanone compounds from a tropical plant and found some to be moderately effective against cancer cells.

## Contribution

The discovery of eight new chromanone derivatives and the first report of chromanone–steroid hybrids in plants.

## Key findings

- Compounds 7 and 8 are the first chromanone–steroid hybrids reported in plants.
- Compounds 6 and 9 showed moderate cytotoxic activity against KB and HeLa S3 cancer cells.
- Compounds 3–5 selectively inhibited KB cell growth with IC50 values between 18.77 and 27.06 μM.

## Abstract

The genus Calophyllum (Calophyllaceae), distributed mainly in tropical regions, is rich in chromanone derivatives with diverse molecular structures that exhibit potential antimicrobial and anticancer effects. Phytochemical investigation of the stem bark of C. calaba collected in Thailand led to the discovery of eight previously undescribed chromanones, calabanones A–H (1‒8), and two known analogs, (‒)-isocalomembranone P (9) and (‒)-calomembranone P (10). The chemical structures of undescribed compounds were elucidated using spectroscopic analyses, particularly NMR and HRESIMS, while their absolute configurations were determined through ECD and NMR calculations combined with DP4+ probability analysis. Compounds 7 and 8 were identified as chromanone–steroid hybrids linked via an ester bond, representing the first report of such structures in plants. Cytotoxic evaluation of the isolated specialized metabolites revealed that compounds 6 and 9 displayed moderate activity against KB and HeLa S3 cancer cell lines, with IC50 values ranging from 12.71 to 25.50 μM, while compounds 3‒5 selectively inhibited the growth of KB cells, with IC50 values in the range of 18.77‒27.06 μM.

The online version contains supplementary material available at 10.1007/s13659-026-00603-5.