Rhopaloic acid

From the Maldives Black marine sponge Hyrtios erectci, several cytotoxic sesterterpenes were isolated, such as the penytacyclic sesterterpenes designated sesterstatins [125-127] and puupehenone, Fig. (18) with a quinone-methide system [128], Three novel cytotoxic nor-sesterterpenes, rhopaloic acid A, Fig. (19), B and C, were recently isolated from the sponge Rhopciloeides sp. 

Addition of sulfur nucleophiles such as phenylthiolate to diethyl l-(ethoxycarbonyl)vinylphos-phonate has been used in the synthesis of P-acetoxy- and p-hydroxy-a-methylene-y-butyrolac-tones Similarly, addition of isopropylthiolate to diethyl l-(ethoxycarbonyl)vinylphosphonate represents a key step in the synthesis of a-methylidenebutyrolactones such as confertin (Scheme arteannuin B, - - rhopaloic acid and hippospongic acid A Addition... 

Nishitani, H., Sasaoka, A., Tokumasu, M., and Ohkata, K., Asymmetric synthesis of rhopaloic acid A analogs and their biological properties. Heterocycles, 50, 35, 1999. 

Intramolecular reaction of allenes is known to proceed mainly by palladation at the central carbon to generate alkenylpalladium 235, which undergoes further reactions. Also TT-allylpalladium 236 is formed when a nucleophile attacks the central carbon. The intramolecular aminopalladation of the 6-aminoallene 237, followed by CO insertion, afforded the unsaturated amino ester 238. The reaction has been applied to the enantioselective synthesis of pumiliotoxin [103]. Oxycarbonylation of the allenyl alcohol 239 afforded the unsaturated ester 240 in 83 % yield using a catalytic amount of PdCl2 and 3 equivalents of CuCb in MeOH and is used for the synthesis of rhopaloic acid [104]. 

Alkoxycarbonylation is also a useful method for allene cyclization (Schemes 6.42)." " " This reaction has been employed in a synthesis of rhopaloic acid by cyclization of allene 6.133 (Scheme 6.43)." ... 

Ohta, S., Uno, M., Yoshimura, M., Hiraga, Y, and Ikegami, S. (1996b) Rhopaloic acid A a novel nor-sesterterpene from a marine sponge, Rhopaloeides sp., which inhibits gastrtdation of starfish embryos. Tetrahedron Lett., 37, 2265-2266. 

Kadota, K. and Ogasawara, K. (2003) A stereocontrolled synthesis of (+)-rhopaloic acid a using a dioxabicyclo[3.2.1]octane chiral building block. Heterocydes, 59, 485-490. 

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