RKS-1778, A NEW MAMMALIAN CELL-CYCLE INHIBITOR AND A KEY INTERMEDIATEOF THE [11]CYTOCHALASIN GROUP

In the course of screening for the mammalian cell-cycle inhibitors, we have isolated a new [11]cytochalasin, RKS-1778 (1), and epoxycytochal asin H (2) from a fungus, Phoma sp. SNF-1778. The structure of 1 was d etermined to be 18-tetramethyl[11]cytochalasa-6,13,19-trien-1-one, on the basis of spectroscopic methods, including H-1- and C-13-2D NMR tec hniques. RKS-1778 (1) may be a precursor of 2 and the key direct produ ct of a proposed biosynthetic intramolecular Diels-Alder reaction. Bot h 1 and 2 completely arrested the cell-cycle progression of tsFT210 ce lls in the M phase at concentrations of 2.1 and 2.0 mu M, respectively .