Influence of rhamnose substituents on the potency of SL0101, an inhibitor of the Ser/Thr kinase, RSK

Jeffrey A. Smith, David J. Maloney, David E. Clark, Yaming Xu, Sidney M. Hecht, Deborah A. Lannigan

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


We have previously reported the isolation of kaempferol 3-O-(3″,4″-di-O-acetyl-α-l-rhamnopyranoside) from Forsteronia refracta [Xu, Y.-M.; Smith, J. A.; Lannigan, D. A.; Hecht, S. M. Biorg. Med. Chem. 2006, 14, 3974-3977.]. This flavonoid glycoside, termed SL0101, is a specific inhibitor of p90 ribosomal S6 kinase (RSK) with a dissociation constant of 1 μM. In intact cells, however, the EC50 for inhibition of RSK activity is 50 μM, which suggests that the efficacy of SL0101 could be limited by cellular uptake. Therefore, we investigated the possibility of developing a more potent RSK inhibitor by synthesizing SL0101 analogs with increased hydrophobic character. The total syntheses of kaempferol 3-O-(3″,4″-di-O-butyryl-α-l-rhamnopyranoside) (Bu-SL0101) and kaempferol 3-O-(2″,3″,4″-tri-O-acetyl-α-l-rhamnopyranoside) (3Ac-SL0101) were performed. The IC50 for inhibition of RSK activity in in vitro kinase assays for the analogs was similar to that obtained for SL0101. 3Ac-SL0101 demonstrated the same remarkable specificity for inhibiting RSK activity in intact cells as SL0101; however, Bu-SL0101 was not completely specific. 3Ac-SL0101 was ∼2-fold more potent at inhibiting MCF-7 cell proliferation compared to SL0101 and preferentially decreased MCF-7 cell growth, as compared to the growth of the normal human breast line, MCF-10A. Thus the discovery of 3Ac-SL0101 as a more potent RSK-specific inhibitor than SL0101 should facilitate the development of RSK inhibitors as anti-cancer chemotherapeutic agents.

Original languageEnglish (US)
Pages (from-to)6034-6042
Number of pages9
JournalBioorganic and Medicinal Chemistry
Issue number17
StatePublished - Sep 1 2006
Externally publishedYes


  • 3Ac-SL0101
  • Bu-SL0101
  • Kaempferol 3-O-(2″,3″,4″-tri-O-acetyl-α-l-rhamnopyranoside)
  • Kaempferol 3-O-(3″,4″-di-O-butyryl-α-l-rhamnopyranoside)
  • Kinase inhibitor
  • RSK

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Medicine
  • Molecular Biology
  • Pharmaceutical Science
  • Drug Discovery
  • Clinical Biochemistry
  • Organic Chemistry


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