(–)-6α-Hydroxy polyanthellin A — A novel antifouling diterpenoid from the Indian soft coral Cladiella krempfi (Hickson)

Abstract

Bioassay-guided purification of methanol extract of the soft coral Cladiella krempfi (Octocorallia: Alcynocea) yielded a novel eunicellin-type diterpenoid, (–)-6α-hydroxy polyanthellin A (1), active against the cyprids of the fouling barnacle, Balanus amphitrite (EC50 9.02 µg/mL; LC50 36 µg/mL; and therapeutic ratio = 4). The structure of compound 1 was determined from its spectral data, including IR, NMR (1D and 2D NMR), and mass spectra.

Marine natural products

“…(À)-6a-Hydroxypolyanthellin A 962 was isolated as a barnacle antifouling constituent of Cladiella kremp (Kavaratti Is., Lakshadweep, India). 677 Diterpenes isolated from a single collection of Cladiella sp. from an unspecied Indonesian location were the subject of three publications in 2011.…”

Antifouling Compounds from Marine Invertebrates

“…AF eunicellin-based diterpenoids ( Figure 6 ): 14-Deacetoxycalicophirin B ( 84 ), astrogorgins B-D ( 85 – 87 ), and analogues 88 – 89 isolated from a gorgonian Astrogorgia sp., exhibited AF activity against B. amphitrite larvae with EC 50 values of 0.59–17.8 μg/mL [ 39 ]. (−)-6α-Hydroxypolyanthelline A ( 90 ) from the soft coral Cladiella krempfi showed toxicity and AF activity against B. amphitrite larvae [ 40 ].…”

Antifouling Eunicellin-Type Diterpenoids from the Gorgonian Astrogorgia sp.

“…Among them, 14-deacetoxycalicophirin B ( 19 ) was the most potent, with an EC 50 = 0.59 μg/mL, whereas the other compounds exhibited moderate or weak inhibition. The therapeutic ratio (LC 50 /EC 50 ) commonly used to assess the effectiveness of a compound in relation to its toxicity should be larger than 15 to select a nontoxic antifouling candidate . The large therapeutic ratio of 19 (>42) suggests that it might be useful as an environmentally benign antifouling agent.…”

“…The therapeutic ratio (LC 50 / EC 50 ) commonly used to assess the effectiveness of a compound in relation to its toxicity should be larger than 15 to select a nontoxic antifouling candidate. 30 The large therapeutic ratio of 19 (>42) suggests that it might be useful as an environmentally benign antifouling agent. This is the second report for the antifouling activities of eunicellin analogues.…”