A novel 9,10-secosterol, astrogorgiadiol (1), and a new eunicellin-based diterpenoid, astrogorgin (2), along with a known eunicellin, ophirin (3), were isolated from the gorgonian Astrogorgia sp., collected at Okino-shima Island off Shikoku, Japan [2] (Table 1). The structures of new metabolites 1 and 2 were established by spectroscopic methods and by comparison of the spectral data with those of related analogs. Compounds 1–3 were found to display activity to inhibit cell division of the fertilized eggs of the starfish Asterina pectinifera.

Furthermore, twenty-one 9,10-secosterols, including thirteen new metabolites, astrogorgols A–M (4–16), along with eight known compounds, calicoferols A–C (17–19), E (20), G (21), I (22), 24-exomethylenecalicoferol E (23), and astrogorgiadiol (1) and a new steroid, astrogorgol N (24), were isolated from the gorgonian Astrogorgia sp. collected from the inner coral reef in Beibuwan Bay, Guangxi province, China [3] (Table 2). The structures of new sterols 4–16 and 24 were determined by spectroscopic methods and by comparison of their spectral and physical data with those reported in the literature. Secosterols 1, 9, 17, 18 and 23 showed inhibitory effects against a series of protein kinases. The structures of calicoferols B (18) [3,4], C (19), E (20) [3,5] and I (22) [3,6] that are shown in reference 3 should be revised as presented in the original literature.

In 1998, a new unstable sesquiterpene, bebryazulene (25), with a guaiane skeleton, was isolated from the gorgonian coral B. grandicalyx, collected at the Prevoyante Reef, Lagoon of Mayotte, Comoros Islands, Indian Ocean [7] (Table 3). The structure of guaiane 25 was assigned by spectroscopic methods. This metabolite was labile and reacted with 4-phenyl-3H-1,2,4-triazoline-3,5-dione to yield a triazolinedione adduct.

B. indica, a gorgonian species collected off the coast of Sanya, Hainan province, China, was found to contain a new steroidal glycoside, bebrycoside (26) [8] (Table 4). The main structure of 26 was determined by spectral data analysis, although the stereochemistry of the C-25 chiral carbon was not determined. Bebrycoside (26) is the first steroidal glycoside to be isolated from the genus Bebryce.

Bebryceoid A (27), a new trihydroxysteroid, was isolated from gorgonian Bebryce sp., collected off the coast of Pingtung, southern Taiwan [9] (Table 5). The structure of steroid 27 was assigned by spectroscopic methods. Bebryceoid A (27) exhibited weak cytotoxicity toward P388D1 and DLD-1 tumor cells.

Two sesquiterpenoids, including new natural product (7S,10R)-(+)-10,11-epoxycurcuphenol (28) and known metabolite (+)-curcuphenol (29) [10], along with a new labdane-type diterpenoid, echinolabdane A (30), a new sterol, 6-epi-yonarasterol B (31) [11], a new clerodane-type diterpenoid, echinoclerodane A (32) [12] and a new halimane-type diterpenoid, echinohalimane A (33) [13], were isolated from the gorgonian coral Echinomuricea sp., collected off the coast of southern Taiwan (Table 6). The structures of metabolites 28–33 were elucidated by spectroscopic methods. Echinolabdane A (30) possesses a novel tetracyclic skeleton with an oxepane ring joined to an α,β-unsaturated-γ-lactone ring by a hemiketal moiety [11]. Echinolabdane A (30), echinoclerodane A (32) and echinohalimane A (33) are the first labdane-, clerodane- and halimane-type diterpenoids to be obtained from marine organisms belonging to the phylum Cnidaria, respectively [11,12,13].

In biological activity experiments, sesquiterpenoid 29 displayed a significant inhibitory effect on the release of elastase by human neutrophils. This compound also exhibited weak cytotoxicity toward DLD-1 and CCRF-CEM tumor cells [9]. Steroid 31 displayed significant inhibitory effects on the generation of superoxide anions and the release of elastase by human neutrophils [11]. Clerodane 32 exhibited weak cytotoxicity toward MOLT-4 and HL-60 tumor cells and displayed a significant inhibitory effect on the generation of superoxide anions by human neutrophils [12]. Halimane 33 exhibited cytotoxicity toward K562, MOLT-4, HL-60, DLD-1 and LoVo tumor cells and displayed a significant inhibitory effect on the release of elastase by human neutrophils [13].

Four new steroids of the cholestane class, anastomosacetals A–D (34–37), were obtained from the gorgonian coral E. anastomosans, collected off the shore of Keomun Island, South Sea Korea [14] (Table 7). The structures of steroids 34–37 were determined by spectroscopic methods, and these four compounds are the first examples of marine steroids possessing an unusual hemiacetal linkage formed by oxidation of the C-21 methyl group.

In addition, seven new moritoside class farnesylhydroquinone glycosides, euplexides A–G (38–44), were isolated from E. anastomosans [15,16] (Table 7). The structures of glycosides 38–44, including their absolute stereochemistry, were elucidated by spectroscopic and chemical methods. Compounds 38–44 exhibited moderate cytotoxicity and antioxidant activity as well as an inhibitory effect against PLA₂.

A prostaglandin derivative, PGF_2α (45), was isolated from the gorgonian coral E. erecta collected at Shimoda, Sagami Bay, Japan [17] (Table 8), and this compound was proven to be the active component in E. erecta. This finding is the first demonstration that gorgonian corals containing prostaglandins are not limited to species in the Caribbean area.

Furthermore, a bluish-violet oil, guaiazulene (46), was isolated from E. erecta collected at Enoshima Island, Kanagawa, Japan [18] (Table 8). The structure of guaiazulene (46) from E. erecta was determined by spectroscopic methods and by comparison of the spectral data with those of reported data. This is the first isolation of guaiazulene from an animal, and this compound showed mild antimicrobial activity [18].

Four new unnamed fatty acid derivatives 47–50, which contain a butenolide moiety, were isolated from the gorgonian coral E. flava, collected at the coral reef of Ishigaki Island, Okinawa, Japan. The structures of butenolides 47–50 were elucidated by spectroscopic and chemical methods [19] (Table 9).

Six new tetraprenylated purine alkaloids, nuttingins A–F (51–56), were isolated together with five new compounds, malonganenones D–H (57–61), and three known metabolites, malonganenones A–C (62–64), from the gorgonian coral E. nuttingi collected in Uvinage, Pemba Island, Tanzania. The structures of compounds 51–64 were elucidated by interpretation of spectral data [20] (Table 10). Mixtures of nuttingins A and B (51 and 52), C–E (53–55), malonganenones D and E (57 and 58), and F and G (59 and 60) have been found to inhibit growth of K562 and UT7 tumor cells. Nuttingins A–E (51–55) and malonganenones D–H (57–61) induce apoptosis in transformed mammalian cells [20].

Moritoside (65), a new hydroquinone glycoside derivative was isolated from the gorgonian Euplexaura sp., collected near Morito beach in the Gulf of Sagami, Japan. The structure of glycoside 65 was determined by spectroscopic and chemical methods [21] (Table 11). This is the first example of the occurrence of D-altrose in natural products, and this compound inhibits the first cell division of fertilized starfish (Asterina pectinifera) eggs.

The gorgonian M. spinifera collected off the South China Sea was found to contain six known compounds, including batyl alcohol (66) [22,23], picolinic acid N-methyl betaine (67) [23,24], n-hexadecanol (68) [23], 3β-hydroxy-5α-pregnane-20-one (69) [23], 9H-purin-6-amino-N-9-dimethyl (70) [23] and thymidine (71) [23] (Table 12). The structures of compounds 66–71 were elucidated by spectroscopic methods.

Four new highly-oxygenated guaiane lactones, menverins A–D (72–75) [25], and two new polyoxygenated steroids, menellsteroids A (76) and B (77) [26] (Table 13), were isolated from the gorgonian M. verrucosa, collected along the coast of Xiaodong Hai, Hainan province, China. The structures of metabolites 72–77 were established by spectroscopic methods. In a later study, menellsteroid A (76) was found to exhibit modest anti-inflammatory inhibition of lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW264.7 macrophages [27].

Li et al., isolated four new highly-oxygenated guaiane lactones, 1-epimenverin B (78), menverin F (79), 1-deoxymenverin F (80) and menverin G (81), along with two known guaiane analogs, menverins B (73) and C (74), from the gorgonian Menella sp., collected off the Lingshui Bay, Hainan province, China [28] (Table 14). The structures of new guaianes 78–81 were elucidated by spectroscopic methods and by comparison with those of known analogs.

A chemical investigation of the gorgonian Menella sp., collected off Meishan Island, Hainan province, China, resulted in a novel highly-oxygenated racemate with a C8 skeleton, menellin A (82), a new tetrahydroxysteroid, menellsteroid C (83), a new natural product, 1β,3β,5α-trihydroxy-cholestan-6-one (84) and seven known compounds, menellsteroid A (76), cholestan-3β,5α,6β-triol (85), cholestan-1β,3β,5α,6β-tetrol (86), nephalsterol (87), cholestan-3β-5-en-6-one (88) and junceellolides B (89) and D (90) [27] (Table 15). The structures of the above compounds were elucidated by spectroscopic methods and by comparison of the spectral data with those of known analogs. The structure, including the relative stereochemistry, of menellin A (82) was further confirmed by single-crystal X-ray diffraction analysis. As already reported for menellsteroid A (76), menellin A (82) exhibited modest anti-inflammatory inhibition of lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW264.7 macrophages.

Seven pregnane steroids, 3α-hydroxy-5β-pregnan-20-one (91), 3β-hydroxy-5α-pregnan-20-one (92), 3β-hydroxy-pregnan-5-en-20-one (93), 5β-pregnan-3,20-dione (94), 5α-pregnan-3,20-dione (95), pregnan-4-en-3,20-dione (96) and pregnan-1,4-dien-3,20-one (97), were isolated from the gorgonian Menella sp., collected off Meishan Island, Sanya Bay, Hainan province, China [29] (Table 16). The structures of steroids 91–97 were elucidated by spectroscopic methods and by comparison with those of known analogs. The NMR data of steroid 97 are reported for the first time in this study.

Eight sesquiterpenoids, including seven new compounds, (–)-hydroxylindestrenolide (98) [30], menelloides A–E (99–103) [31,32,33] and (+)-chloranthalactone B (104) [31], along with a known metabolite, seco-germacrane anhydride (105) [34] (Table 17), were isolated from the Formosan gorgonian Menella sp., collected by trawling off the coast of southern Taiwan. (–)-Hydroxy-lindestrenolide (98) and (+)-chloranthalactone B (104) were proven to be enantiomers of the known sesquiterpenoids (+)-hydroxylindestrenolide and chloranthalactone B, respectively [30,31]. Menelloide A (99) was found to possess a new carbon skeleton [31]. Seco-germacrane anhydride (105) was a known metabolite and there have been no reports of seco-germacrane anhydride (105) being obtained from any marine organism previously [34]. Several of these compounds displayed inhibitory effects on the generation of superoxide anions and the release of elastase by human neutrophils.