*Article* **A Great Barrier Reef** *Sinularia* **sp. Yields Two New Cytotoxic Diterpenes**

**Anthony D. Wright †, Jonathan L. Nielson ‡, Dianne M. Tapiolas, Catherine H. Liptrot § and Cherie A. Motti \***

Australian Institute of Marine Science, PMB no. 3, Townsville MC, Townsville, QLD 4810, Australia; adwright@hawaii.edu (A.D.W.); jonathon.nielson@acdlabs.com (J.L.N.); d.tapiolas@aims.gov.au (D.M.T.); catherine.liptrot@jcu.edu.au (C.H.L.)

**\*** Author to whom correspondence should be addressed; c.motti@aims.gov.au; Tel.: +61-7-47534143; Fax: +61-7-47725852.

Received: 4 June 2012; in revised form: 25 June 2012; Accepted: 23 July 2012; Published: 31 July 2012

**Abstract:** The methanol extract of a *Sinularia* sp., collected from Bowden Reef, Queensland, Australia, yielded ten natural products. These included the new nitrogenous diterpene (4*R*\*,5*R*\*,9*S*\*,10*R*\*,11*Z*)-4-methoxy-9-((dimethylamino)-methyl)-12,15-epoxy-11(13)-en-decahydronaphthalen-16-ol (**1**), and 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**). Also isolated were two known cembranes, sarcophytol-B and (1*E*,3*E*,7*E*)-11,12-epoxycembratrien-15-ol, and six known lobanes, loba-8,10,13(15)-triene-16,17,18-triol, 14,18-epoxyloba-8,10,13(15)-trien-17-ol, lobatrientriol, lobatrienolide, 14,17-epoxyloba-8,10,13(15)-trien-18-ol-18-acetate and (17*R*)-loba-8,10,13(15)-trien-17,18-diol. Structures of the new compounds were elucidated through interpretation of spectra obtained after extensive NMR and MS investigations and comparison with literature values. The tumour cell growth inhibition potential of **1** and **2** along with 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 were assessed against three human tumour cell lines (SF-268, MCF-7 and H460). The lobanes and cembranes tested demonstrated 50% growth inhibition in the range 6.8–18.5 μM, with no selectivity, whilst **1** was less active (GI50 70–175 μM).

**Keywords:** *Sinularia*; Alcyoniidae; anticancer activity; lobane; cembrane; diterpene
