Short Approach Towards New Isocoumarins and Dihydroisocoumarins and Investigation of their Cytotoxic Activities

Isocoumarins are a large and structurally diverse class of bioactive natural products with widespread occurance in living organisms [1], and considerable work has been published over decades about their chemistry [2] and biology [3]. A considerable number of natural and synthetic isocoumarins showed significant cytotoxic and antitumor activity. Among those are dihydroisocoumarins like AI-77-B (A), as well as numerous isocoumarins bearing substituents at C-3 (Fig. 1). The dihydroisocoumarin AI-77-B (A) shows in vitro cytotoxicity against human malignant A375S2 and human cervical cancer HeLa cells [4]. The paraphaeosphaerins (B) recently isolated from cultures of Paraphaeosphaeria quadriseptana [5] are biogenetically related to the cytotoxic plant metabolites monocillin I and radicicol. NM-3 (C) is a synthetic analog of cytogenin (E), and potentiates antineoplastic effects of other chemotherapeutic agents and inhibits angiogenesis [6]. This compound is in phase I clinical trials. The isocoumarin 185322 (D) [7], an analog of NM-3, is an inhibitor of microtubule assembly, and induces mitotic arrest and apoptosis of multiple myeloma cells. The biological activities of the abovementioned and other isocoumarins and dihydroisocoumarins [8, 9] make this class of compounds interesting leads for development of new anticancer drugs. The most prominent structural features found in the bioactive com-