ChemInform Abstract: Enantioselective Chiral Borane‐Mediated Aldol Reactions of Silyl Ketene Acetals with Aldehydes. Novel Effect of the Trialkylsilyl Group of the Silyl Ketene Acetal on the Reaction Course.

Kiyooka, Syun‐ichi; Kaneko, Yuichi; Komura, M.; Matsuo, H.; Nakano, Masato

doi:10.1002/chin.199133145

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“…The enantioselective chiral borane-mediated aldol reaction developed by Kiyooka 13 was used to construct the β-hydroxy-α,α-dimethyl acid part of C34- gem -dimethyl acid 4c (Scheme 3 b). Treatment of aldehyde 7 with methyl trimethylsilyl dimethylketene acetal at −78 °C in the presence of chiral oxazaborolidinone 22 (derived from d -Val) provided ( S )-β-hydroxy ester 23 .…”

Section: Resultsmentioning

confidence: 99%

Improved Total Synthesis and Biological Evaluation of Potent Apratoxin S4 Based Anticancer Agents with Differential Stability and Further Enhanced Activity

et al. 2014

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Apratoxins are cytotoxic natural products originally isolated from marine cyanobacteria that act by preventing cotranslational translocation early in the secretory pathway to downregulate receptor levels and inhibit growth factor secretion, leading to potent antiproliferative activity. Through rational design and total synthesis of an apratoxin A/E hybrid, apratoxin S4 (1a), we have previously improved the antitumor activity and tolerability in vivo. Compound 1a and newly designed analogues apratoxins S7–S9 (1b–d), with various degrees of methylation at C34 (1b,c) or epimeric configuration at C30 (1d), were efficiently synthesized utilizing improved procedures. Optimizations have been applied to the synthesis of key intermediate aldehyde 7 and further include the application of Leighton’s silanes and modifications of Kelly’s methods to induce thiazoline ring formation in other crucial steps of the apratoxin synthesis. Apratoxin S9 (1d) exhibited increased activity with subnanomolar potency. Apratoxin S8 (1c) lacks the propensity to be deactivated by dehydration and showed efficacy in a human HCT116 xenograft mouse model.

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Section: Resultsmentioning

confidence: 99%