Chemistry and bioactivity of secondary metabolites from South China Sea marine fauna and flora: recent research advances and perspective

Abstract

Marine organisms often produce a variety of metabolites with unique structures and diverse biological activities that enable them to survive and struggle in the extremely challenging environment. During the last two decades, our group devoted great effort to the discovery of pharmaceutically interesting lead compounds from South China Sea marine plants and invertebrates. We discovered numerous marine secondary metabolites spanning a wide range of structural classes, various biosynthetic origins and various aspects of biological activities. In a series of reviews, we have summarized the bioactive natural products isolated from Chinese marine flora and fauna found during 2000-2012. The present review provides an updated summary covering our latest research progress and development in the last decade (2012-2022) highlighting the discovery of over 400 novel marine secondary metabolites with promising bioactivities from South China Sea marine organisms.

Keywords: biological activity; marine flora; marine natural products; mollusks; soft corals; sponges.

Fig. 1

Structures of new isolates from marine algae.

Fig. 2

Structures of representative compounds from mangroves.

Scheme 1

Possible biosynthesis of acanthiline A (26) in Acanthus ilicifolius.

Fig. 3

Structures of new bioactive isolates from sponges.

Scheme 2

Biomimetic synthetic route of 33 and 34.

Fig. 4

Structures of representative compounds from soft corals of Lobophytum.

Fig. 5

Structures of representative sesquiterpenoids from soft corals of Sinularia.

Fig. 6

Structures of representative Cembrane diterpenoids and related rare diterpenoids (62, 71 and 72) from soft corals of Sinularia.

Fig. 7

Structures of representative Casbane diterpenoids and related rare diterpenoids (84 and 85) from soft corals of Sinularia.

Scheme 3

Chemical correlation of compounds 82 and 83.

Scheme 4

The plausible biosynthetic connection of cembranes, casbanes, sinueretone A (84) and sinunanolobatone A (85).

Fig. 8

Structures of other uncommon diterpenoids (86–98) from soft corals of Sinularia.

Fig. 9

Structures of novel representative steroids from soft corals of Sinularia.

Fig. 10

Structures of novel representative biocembranoids from soft corals of Sarcophyton.

Scheme 5

The plausible endo/exo-Diels-Alder Cycloaddition.

Fig. 11

Structures of some representative compounds from soft corals of Sarcophyton.

Fig. 12

Structures of compounds 121–125.

Scheme 6

Proposed biosynthetic pathway of compound 121.

Scheme 7

Proposed biosynthetic pathway of compounds 124 and 125.

Fig. 13

Structures of representative compounds from soft corals Litophyton nigrum, Lemnalia flava, Clavularia viridis, Cladiella krempfi, and Klyxum flaccidum.

Fig. 14

Structures of representative compounds from nudibranches.

Fig. 15

Structures of compounds 150–153 isolated from the marine sacoglossan Placobranchus ocellatus.

Scheme 8

Proposed photobiosynthetic pathway towards novel polyketides 150–153.

Scheme 9

Biomimetic semisynthesis of ocellatusone A (150) from natural precursor 154.

Fig. 16

Structures of compounds 156–158 isolated from the marine pulmonate Onchidium sp.