Sorazolons, Carbazole Alkaloids from <i>Sorangium cellulosum</i> Strain Soce375

Sorazolons A (<b>1</b>) to E2 (<b>9</b>) were isolated from <i>Sorangium cellulosum</i> strain Soce375. Their molecular structures were elucidated using extensive HRESIMS and NMR analysis. The absolute configuration of sorazolon A (<b>1</b>) was determined by comparison of the experimental CD spectrum with quantum chemical calculated spectra for both enantiomers. Sorazolons D2 (<b>7</b>), E (<b>8</b>), and E2 (<b>9</b>) exhibit a moderate cytotoxic activity against mouse fibroblast cell line L929 with IC₅₀ values between 5.0 μM and 0.09 mM