Neolemnane-Type Sesquiterpenoids from a Formosan Soft Coral Paralemnalia thyrsoides

Abstract

Soft corals belonging to the genera Paralemnalia [1][2][3][4] and Lemnalia [5][6][7][8][9][10][11][12] have been found to be a rich source of neolemnane and nardosinane sesquiterpenoids. Our previous investigation on the chemical constituents of a soft coral Paralemnalia thyrsoides has resulted in the isolation of three terpenoids, paralemnolins A-C.13) Continuing study on searching new metabolites of this soft coral again afforded six new metabolites paralemnolins D-I (1-6) (neolemnanoids). We describe herein the isolation, structure elucidation and biological activity of these compounds. Results and DiscussionParalemnolin H COSY spectrum was used to reveal the connectivity of H-4/H-5, H-5/H 2 -6, H 2 -6/H 2 -7, H-9/H 2 -10, and H 2 -10/H 2 -11 (Fig. 1). The vinyl methyl [d 1.57 (3H, d, Jϭ1.2 Hz)] attached at C-3 was confirmed by the HMBC correlations from H 3 -14 to C-2, C-3 and C-4. The methyl group attached at C-1 and the connectivities from C-7 to C-8 and C-8 to C-9 were deduced from the following HMBC correlations: H 3 -13/C-1, C-2, C-8, C-12 and H 2 -7/C-8, C-9. Moreover, a methyl [d 0.87 (3H, d, Jϭ6.6 Hz)] attached at C-12 was confirmed by the HMBC correlations from H 3 -15 to C-1, C-11, and C-12. The placement of the acetyl group at C-4 was confirmed by the HMBC correlation of H-4 (d 6.49) with C-3 and the carbonyl group of ester. Thus, the hydroxyl group should be positioned at C-5, and the planar structure of 1 was established. The relative stereochemistry and detailed 1 H-NMR data assignment of 1 were elucidated from the NOE correlations observed in a NOESY experiment (Fig. 2). The Z geometry of the 2,3-double bond was established by an NOE interaction between H-2 and H 3 -14. Also, H 3 -13 was found to show NOE interactions Six new sesquiterpenoids, paralemnolins D-I (1-6), have been isolated from the EtOAc extract of the soft coral Paralemnalia thyrsoides. The structures of these metabolites were determined by extensive spectroscopic analysis and by comparison of their spectral data with those of related metabolites. The absolute stereochemistry of these metabolites was established by application of the Mosher's method on 1 and on the basis of the absolute structures of other related compounds previously isolated from the soft corals of the genera Paralemnalia and Lemnalia. Cytotoxicity of these metabolites toward a limited panel of cancer cell lines also is reported.

Parathyrsoidins A–D, Four New Sesquiterpenoids from the Soft Coral Paralemnalia thyrsoides

“…13α-Methylated nardosinane-type metabolites have been found in soft corals Lemnalia africana and Nephthea elongata [2,4]. …”

“…Soft corals belonging to the genus Paralemnalia have been proved to be a rich source of sesquiterpenoids [1,2,3,4,5,6,7,8,9,10,11,12,13]. Our recent study of the chemical constituents of the soft coral P. thyrsoides has yielded a cytotoxic bisnorsesquiterpenoid, paralemnolide A [13].…”

Paralemnolide A, an Unprecedented Bisnorsesquiterpene from the Taiwanese Soft Coral Paralemnalia thyrsoides

“…Soft corals of the genus Paralemnalia [1,2,3,4,5,6,7,8] have been found to be rich sources of sesquiterpenoids of nardosinane [1,2,3], neolemnane [3,4] and africanane-type [3] compounds, as well as norsesquiterpenoids of nornardosinane-type [3,5,6] compounds. As part of the continuing search for bioactive substances from marine invertebrates, we explored the secondary metabolites of the soft coral Paralemnalia thyrsoides (Ehrenberg, 1934) which was collected from Sansiantai, Taitong County, Taiwan (Figure 1).…”

Nardosinane-Type Sesquiterpenoids from the Formosan Soft Coral Paralemnalia thyrsoides

“…Soft corals of the genus Paralemnalia [1–7] and Lemnalia [8–12] have been found to be rich sources of sesquiterpenoids of nardosinane [1–3,9,12,13], neolemnane [3,4,10,11] and africanane-type [3,8] compounds and norsesquiterpenoids of nornardosinane-type [3,5,6,9,10] compounds. Our previous study on the secondary metabolites of a Taiwanese soft coral Paralemnalia thyrsoides , collected from the coast of Green Island, has resulted in the isolation of two norsesquiterpenoids [6], ten sesquiterpenoids [4,6,7] and three novel sesquiterpenoids derived from a nardosinane precursor [7].…”

“…Our previous study on the secondary metabolites of a Taiwanese soft coral Paralemnalia thyrsoides , collected from the coast of Green Island, has resulted in the isolation of two norsesquiterpenoids [6], ten sesquiterpenoids [4,6,7] and three novel sesquiterpenoids derived from a nardosinane precursor [7]. In our continuing search for new and bioactive metabolites from Formosan soft corals, Paralemnalia thyrsoides collected from Orchid Island were chemically investigated for the first time, and the investigation has resulted in the isolation of five new nardosinane-type sesquiterpeneoids, paralemnolins Q–U ( 1 – 5 ), along with three known compounds 2-deoxylemnacarnol ( 6 ) [2], 2-deoxy-7- O -methyllemnacarnol ( 7 ) [14] and 2-oxolemnacarnol ( 8 ) [15] (Chart 1).…”