A New Bisindole from Alga Caulerpa serrulata

Abstract

A new bis-indole, caulersin (4), was isolated from the alga Caulerpa serrulata, collected from the Xisha Islands in the South China Sea. The structure was established by spectroscopic methods.

Screening marine algae from China for their antitumor activities

“…And certain marine algae, such as Ecklonia kuroma and Sargassum fusiforme, have been used in traditional Chinese herbal medicine in treatment of cancer. But only a few new natural products have been isolated from algae in the South China Sea (Su et al, 1997). None relate to antitumor screening and new antineoplastic compounds of the marine algae in North China.…”

Marine Bi-, Bis-, and Trisindole Alkaloids

“…Chloromethylenemorpholinium chloride-mediated cyclization followed by DMSO oxidation yielded 177. Wahlström et al also obtained the crystal structure of 177, confirming that the chemical structures of both their synthetic product and that proposed for the natural product 105 were the same. The NMR spectral data obtained for the product from both synthetic procedures earlier 117,118 were virtually identical; however, when these data were compared with those of the natural product, several differences especially in the 13 were observed.…”

“…103 Only three naturally occurring marine analogs of 173 have been reported: the diacid 174 and monoacid 175 92 and the recently discovered halogenated caulerchlorin (176), all three of which were isolated from C. racemosa. 104 Cleome serrulata yielded the first example of a troponoid-fused bisindole, which was given the trivial name caulersin (177) 105 (Figure 1.15 The distribution of 173 was assessed in several species of Caulerpa collected from the coasts of Bermuda, Florida, and Tasmania. 106 The Caulerpa genus has classically been divided into two major albeit tenuous groups, the frond-like bilateral leaf species, which grow below the littoral zone in relatively still water, and the radially branched species, which characteristically prefer habitats associated with the brighter shallower but turbulent littoral zone.…”

“…The NMR spectral data obtained for the product from both synthetic procedures earlier 117,118 were virtually identical; however, when these data were compared with those of the natural product, several differences especially in the 13 were observed. 105 Wahlström et al attributed these differences to the low signal-to-noise ratio evident in the 13 C spectrum of the natural product (because of a paucity of isolated material), which could have obscured the C-11 signal at d C 119.3 and led to an incorrect assignment of C-20 at d C 114.6 instead of d C 146. 105,118 In an attempt to clarify the reason for the ambiguities in the NMR data of 177, Miki et al 119 developed a procedure to synthesize 177 (Scheme 1.34) and three isomers (184-186) of 177 (Scheme 1.35) starting from variably protected indolecarboxylic anhydrides and coupling them to a series of methyl indoleacetates, followed by cyclization.…”

“…105 Wahlström et al attributed these differences to the low signal-to-noise ratio evident in the 13 C spectrum of the natural product (because of a paucity of isolated material), which could have obscured the C-11 signal at d C 119.3 and led to an incorrect assignment of C-20 at d C 114.6 instead of d C 146. 105,118 In an attempt to clarify the reason for the ambiguities in the NMR data of 177, Miki et al 119 developed a procedure to synthesize 177 (Scheme 1.34) and three isomers (184-186) of 177 (Scheme 1.35) starting from variably protected indolecarboxylic anhydrides and coupling them to a series of methyl indoleacetates, followed by cyclization. 119 They went on to compare the 13 C NMR data of synthetic 177 and 184-186 with those reported for the natural product and found that while the NMR data of their synthetic caulersin matched those of the previously reported syntheses of this compound, neither the NMR data of their synthetic 177 nor the three isomers matched the NMR data of the natural product.…”