A carbazole-pyranocoumarin conjugate, carbazomarin B (1), and two carbazole alkaloids, 6-methoxymukonidine (2) and 2-hydroxy-3-methoxycarbazole (3), together with 27 known compounds (4-30), were isolated from the stems of Clausena excavata. Their structures have been elucidated by spectroscopic analyses. Compound 2 showed moderate cytotoxicity to HuCCA-1, MOLT-3 and HepG2 cancer cell lines with IC50 values of 15.09-28.50 μg/mL, but none to A549 cell line. Heptaphylline (6) and nordentatin (23) were found to show moderate cytotoxic activity against HepG2 cell line with IC50 values of 12.33 and 11.33, respectively, while clausine K (27) exhibited strong cytotoxicity with IC50 value of 1.05 μg/mL, better than a standard drug (etoposide, IC50 13.40 μg/mL).

The formal synthesis of (+)-3-epi-eupomatilone-6 () and the 3,5-bis-epimer () has been accomplished. The key synthetic strategy involved the stereoselective construction of (3R,4S,5R)- and (3R,4S,5S)-trisubstituted γ-butyrolactones and from (2R,3R)-2,3-dimethyl-4-pentenoic acid derivative , which was readily obtained via stereoselective conjugate addition of vinylmagnesium chloride to a chiral α,β-unsaturated N-acyl oxazolidinone (Evans' auxiliary) followed by α-methylation.

The diastereoselective reaction of the vicinal dianion, generated from di-(−)-menthyl succinate, with electrophiles, i.e. symmetrical ketones, aldehydes, and benzyl bromide was examined. The reactions with ketones and benzyl bromide gave products in good yields, however, with poor diastereoselectivities. The reaction with aldehydes in the presence of ZnCl 2 preferably gave the anti-aldol adducts, which subsequently led to cis-paraconic esters again with moderate diastereoselectivity.