**1. Introduction**

There have been many reports documenting the diversity of secondary metabolites produced by soft corals from the genus *Sinularia*, including sesquiterpenes [1,2], diterpenes [3–7], cembranoids [8– 11], polyhydroxylated steroids [12], glycosides [13], sphingosines [14], farnesyl quinols [15,16], and polyamines [17]. These metabolites have been shown to possess a range of biological activities including antimicrobial [5], antiviral [4], anti-inflammatory [4,11], cytotoxic [8–10,17], anticancer [3,18], antifouling [19], antifeedant [20], and allelopathic [21,22] activities. Given this wide-ranging diversity in chemical structure and biological activity, it is not surprising that soft corals, which do not have a hard calcareous skeleton, are relatively well defended against predation [20] and are effective competitors for space on coral reefs [21]. As a result, the *Sinularia* genus remains an attractive target for the discovery of novel bioactive metabolites.

As part of the biodiscovery program at the Australian Institute of Marine Science (AIMS), the ethanol (EtOH) extract of a Great Barrier Reef soft coral *Sinularia* sp., was determined to have significant activity in the NCI 60 cell line COMPARE analysis [23]. Based on this, the sample

was selected for recollection, large scale extraction and workup. The methanol (MeOH) extract of the recollected soft coral tissue was subjected to bioassay-guided fractionation, using C18 flash vacuum liquid chromatography and preparative C18 HPLC, to yield the new nitrogenous diterpene (4*R*\*,5*R*\*,9*S*\*,10*R*\*,11*Z*)-4-methoxy-9-((dimethylamino)-methyl)-12,15-epoxy-11(13)-endecahydronaphthalen-16-ol (**1**), the new lobane, (1*R\**,2*R\**,4*S\**,15*E*)-loba-8,10,13(14),15(16)-tetraen-17, 18-diol-17-acetate (**2**), and eight known diterpenes: two cembranes, sarcophytol-B [24] and (1*E*,3*E*,7*E*)-11,12-epoxycembratrien-15-ol [8], and six known lobanes, loba-8,10,13(15)-triene-16,17,18-triol [25], 14,18-epoxyloba-8,10,13(15)-trien-17-ol [26], lobatrientriol [7], lobatrienolide [7], 14,17-epoxyloba-8,10,13(15)-trien-18-ol-18-acetate [26] and (17*R*)-loba-8,10,13(15)-trien-17,18-diol [27]. The structural elucidation and biological activities of **1**, **2** and of the known compounds loba-8,10,13(15)-triene-16,17,18-triol, 14,17-epoxyloba-8,10,13(15)-trien-18-ol-18-acetate, lobatrienolide, (1*E*,3*E*,7*E*)-11,12-epoxycembratrien-15-ol and sarcophytol-B against a panel of human tumour cell lines are also presented.
