A Practical Enantioselective Total Synthesis of the Bengamides B, E, and Z
(equation presented) A practical total synthesis of Bengamides B, E, and Z from a common polyol intermediate is described. Consecutive aldol condensations afford a protected polyol thioester side chain suitable for coupling to the Bengamides. A novel chiral phase transfer catalyzed enantioselective alkylation affords the more highly functionalized amino caprolactams required for Bengamides B and Z. Use of the 2-naphthylmethyl ether protecting group, compatible with the boron Lewis acids required for enantioselective aldol condensation, allows direct access to Bengamide B.
Boeckman Jr., Robert K.,Clark, Tammy J.,Shook, Brian C.
p. 2109 - 2112
(2007/10/03)
The development of a convergent and efficient enantioselective synthesis of the bengamides via a common polyol intermediate
An efficient, general synthetic route to the bengamide family of antitumor agents from a common polyol thioester is described. Consecutive aldol condensations afford the protected polyol thioester side chain suitable for coupling to the bengamides. A novel chiral-phase-transfer-catalyzed enantioselective alkylation affords the properly functionalized caprolactams required for the synthesis of more-complex members of the bengamide family. Use of the methyl 2-naphthyl ether protecting group, compatible with the boron Lewis acids required for enantioselective aldol condensation, allows direct access to all the bengamides.
Boeckman Jr., Robert K.,Clark, Tammy J.,Shook, Brian C.
p. 4532 - 4560
(2007/10/03)
Total syntheses of bengamides B and E
Total syntheses of the cytotoxic marine natural products bengamides B and E are described. Both bengamides are prepared via amide coupling of a protected polyhydroxylated lactone intermediate 9 with a suitably substituted aminocaprolactam intermediate. Lactone 9 is prepared in five steps from commercially available α-D-glucoheptonic γ-lactone. The key reactions are a selective deprotection of a 1,2-acetonide in the presence of a 1,3-acetonide and an (E)-selective olefination of an unstable aldehyde using a gem-dichromium reagent. The bengamide B lactam intermediate 10 is prepared in seven steps from commercially available (5R)-5-hydroxy-L-lysine (12). The desired S-configuration at the γ-OH lactam position is established using the Mitsunobu reaction.
Stereoselective Conversion of L-Quebrachitol into a Novel Hydroxylated Caprolactam: Total Synthesis of Bengamide B
The stereoselective synthesis of the novel marine natural product, bengamide B (1), starting from L-quebrachitol (3) is described.The hydroxylated caprolactam portion (2a) in 1 was prepared from (+)-conduramine derivative (7), whose amino functionality wa
Enantioselective total syntheses of bengamides B and E
Convergent total syntheses of two sponge-derived cyclolysine derivatives - bengamides B (1) and E (2) - have been accomplished. The polyhydroxylated side chain common to both natural products was obtained from L-glucose and the hydroxylated caprolactam moiety of 1 was prepared using Evans' oxazolidinone chemistry. In the course of this work a new Horner-Emmons reagent incorporating one of Evans' chiral auxiliaries was developed.
Broka,Ehrler
p. 5907 - 5910
(2007/10/02)
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