Total Synthesis and Properties of the Crambescidin Core Zwitterionic Acid and Crambescidin 359
datasetposted on 16.03.2005, 00:00 by Zachary D. Aron, Larry E. Overman
The total synthesis of the crambescidin core acid 9, crambescidins 359 (8) and 431 (7), and the properties of the crambescidin core are described. A key step of the synthetic route to guanidinium carboxylate 9 is Pd(0) catalyzed cleavage of the ester side chain of pentacyclic cinnamyl ester 15. This ester is also employed to prepare a small library of crambescidin alkaloid analogues that differ in their C14 side chain. The zwitterionic guanidinium carboxylate 9 was shown to readily decarboxylate to form crambescidin 359 (8). Decarboxylation of crambescidin core acid 9 was fastest under basic conditions. In the presence of base, up to eight deuterium atoms can be incorporated into the pentacyclic crambescidin core. Both deuterium incorporation and decarboxylation of crambescidin core acid 9 are the result of facile ring opening of the spirocyclic ether rings of the pentacyclic guanidinium moiety.
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pentacyclic guanidinium moietyspirocyclic ether ringsester side chaindeuterium incorporationCrambescidin 359form crambescidin 359deuterium atomscrambescidin alkaloid analogueszwitterionic guanidinium carboxylate 9pentacyclic crambescidin coreCrambescidin Core Zwitterioniccrambescidin coreguanidinium carboxylate 9pentacyclic cinnamyl ester 15crambescidin core acid 9Total SynthesisC 14 side chaincrambescidins 359ring opening