Design and preparation of serine–threonine protein phosphatase inhibitors based upon the nodularin and microcystin toxin structures: Part 2.1 Synthesis of a functionalised nodularin macrocycle and a stripped-down microcystin macrocycle
作者:Antony B. Maude、Amit P. Mehrotra、David Gani
DOI:10.1039/a702410j
日期:——
Nodularins and microcystins are complex natural isopeptidic
hepatotoxins that serve as subnanomolar inhibitors of the eukaryotic
serineâthreonine protein phosphatases, PP1 and PP2A. In Part 1 (A.
P. Mehrotra, K. L. Webster and D. Gani, J. Chem. Soc.,
Perkin Trans. 1, 1997, preceding paper) each of the key
structural or potentially reactive motifs within each macrocycle type
was assessed as a contributor towards phosphatase inhibitory efficacy
and a stripped-down nodularin-type macrocycle was identified as a
suitable precursor to potentially active synthetic inhibitors.
Subsequently, synthetic routes to the 19-membered nodularin macrocyclic
system were developed, using solution-phase chemistry, which
demonstrated that only certain cyclisation protocols were viable. Here
we describe an extension of this chemistry to provide a 19-membered
nodularin macrocycle,
cyclo-[(3R)-3-hydroxymethyl-β-Ala-(
R)-Glu-α-OMe-γ-Sar-(R)-Asp-
α-OMe-β-(S)-Phe-],
appropriately functionalised with a hydroxymethyl group for the
incorporation of lipophilic side-chains. We also demonstrate that the
25-membered microcystin macrocycle,
cyclo-[β-Ala-(R)-Glu-α-
OMe-γ-Sar-(R)-Ala-(S)-Leu-(
R)-Asp-α-OMe-β-(S)-
Phe-], can be prepared in good yield using similar protocols in which
macrocyclisation is effected through the reaction of the amino group of
the (2S)-phenylalanine residue with the
β-pentafluorophenyl ester of the (2R)-aspartic
acid residue.
结节素和微囊藻毒素是复杂的天然同型肽肝毒素,作为真核丝氨酸-苏氨酸蛋白磷酸酶PP1和PP2A的亚纳摩尔抑制剂。在第一部分(A. P. Mehrotra, K. L. Webster和D. Gani,《化学学会杂志》,珀金斯1号,1997年,前面的论文)中,评估了每种大环类型中每个关键结构或潜在反应性基序对磷酸酶抑制效力的贡献,并确定了一个简化版的结节素型大环作为潜在活性合成抑制剂的合适前体。随后,开发了使用溶液相化学合成19元结节素大环体系的合成路线,这表明只有某些环化方案是可行的。在这里,我们描述了这种化学方法的扩展,以提供一个19元结节素大环,环状-[(3R)-3-羟甲基-β-Ala-(R)-Glu-α-OMe-γ-Sar-(R)-Asp-α-OMe-β-(S)-Phe-],适当地带有羟甲基团以纳入亲脂性侧链。我们还证明了25元微囊藻毒素大环,环状-[β-Ala-(R)-Glu-α-OMe-γ-Sar-(R)-Ala-(S)-Leu-(R)-Asp-α-OMe-β-(S)-Phe-],可以使用类似的方案以良好产率制备,其中大环化是通过(2S)-苯丙氨酸残基的氨基与(2R)-天冬氨酸残基的β-五氟苯酯的反应实现的。