Cytotoxic Eunicellin-Type Diterpenes from the Soft Coral Litophyton viscudium

Five new eunicellin-type diterpenes were isolated from the soft coral Litophyton viscudium.The structures of the compounds were elucidated mainly on the basis of extensive spectroscopic analysis.Compounds exhibited cytotoxic activity against HL-60 with IC 50 values of 4.2-50 µM.The soft coral Litophyton species is known to produce a sesquiterpene, 1 cembranes, 1 eunicellin-based diterpenes, 2-5 and sterols 6 possessing biological activities, such as antiproliferative activity against the cell lines L-929 and K-562, cytotoxicity against HeLa cells, 1 and hemolytic, 2 molluscicidal, 3 repellent, 4 insect growth inhibitory, 5 brine shrimp lethality, 6 and antileukemic 7 activities.As a continuation of our survey on bioactive compounds from marine organisms, 8 the CH 2 Cl 2 -soluble portion (23 g) of a MeOH extract of the soft coral L. viscudium (5.3 kg, wet wt.), collected in the area of Otsuki Town area, Kochi Prefecture, Japan, showed moderate cytotoxic activity (IC 50 = 6.9 µg/mL) against the proliferation of human promyelocytic leukemia cells (HL-60).Further investigation of this CH 2 Cl 2 fraction has led to the + H] + (calcd for C 24 H 39 O 5 , 407.2797).Compound (5): amorphous powder; [#] 25 D +33.4 (c 0.35, MeOH); TLC R f 0.55 (3:97, MeOH/CH 2 Cl 2 ); 2154 HETEROCYCLES, Vol.83, No. 9, 2011 IR (NaCl) & max 3495, 1736, 1645 cm -1 ; 1 H NMR and 13 C NMR, see Table 1; HRFABMS m/z 445.2917 [M + Na] + (calcd for C 25 H 42 O 5 Na, 445.2920), m/z 421.2958 [M -H] + (calcd for C 25 H 41 O 5 , 421.2954).Litophynin F (6): amorphous powder; [#] 25 D +12.4 (c 0.28, MeOH); TLC R f 0.28 (1:99, MeOH/CH 2 Cl 2 ); & max 3614, 1734, 1644 cm -1 ; HRFABMS m/z 391.2845 [M + H] + (calcd for C 24 H 39 O 4 , 391.2848).Cell lines.Human leukemia HL-60 cells were maintained in RPMI1640 containing 10% fetal calf serum, 2 mM glutamine and the antibiotic/antimycotic solution at 37 °C in a 5 % CO 2 humidified atmosphere.