SUMMARY Protein synthesis plays an essential role in cell proliferation, differentiation and survival. Inhibitors of eukaryotic translation have entered the clinic, establishing the translation machinery as a promising target for chemotherapy. A recently discovered, structurally unique marine sponge-derived brominated alkaloid, (-)-agelastatin A (AglA), possesses potent antitumor activity. Its underlying mechanism of action, however, has remained unknown. Using a systematic top-down approach, we show that AglA selectively inhibits protein synthesis. Using a high-throughput chemical footprinting method, we mapped the AglA-binding site to the ribosomal A site. A 3.5-Å crystal structure of the 80S eukaryotic ribosome from S. cerevisiae in complex with AglA was obtained, revealing multiple conformational changes of the nucleotide bases in the ribosome accompanying the binding of AglA. Together, these results have unraveled the mechanism of inhibition of eukaryotic translation by AglA at atomic level, paving the way for future structural modifications to develop AglA analogs into novel anticancer agents.

(−)-Agelastatin A (AglA, 1), a member of the pyrrole-aminoimidazole marine alkaloid (PAI) family, possesses a unique tetracyclic structure and is one of the most potent anticancer PAIs isolated to date. In efforts to expand the SAR of these agents and delineate sites that tolerate modification while retaining activity, we synthesized several derivatives and tested their anticancer activity. The cytotoxic effects of these derivatives were measured against several cancer cell lines including cervical cancer (HeLa), epidermoid carcinoma (A431), ovarian (Igrov and Ovcar3), osteosarcoma (SJSA1), acute T cell leukemia (A3), epidermoid carcinoma (A431) in addition to primary human chronic lymphocytic leukemia cells. New positions for modification of AglA and new substitutions were explored leading to novel derivatives, 14-chloro AglA (3) and 14-methyl AglA (12), that retained activity toward various cancer cell lines with decreased toxicity toward B- and T-cells. The SAR data informed the synthesis of a trifunctional probe bearing an alkyne and a diazirine potentially useful for cellular target identification.

A new and flexible approach toward the synthesis of 6,12-guaianolide anticancer drugs such as trilobolides or thapsigargin has been developed that could be applied to the preparation of analogues with a modified ring system. The synthesis starts from commercial 2-methylcyclopentane-1,3-dione, only relying on diastereoselective reactions for the construction of the stereogenic centers at C1, C3, C6, and C10 and features a high-yielding ring-closing enyne metathesis (RCEYM) step for the formation of the [5,7] bicyclic core.