A SuRE way to synthesise macrocyclic peptides

从根本上说，该项目是基于“连续环扩展”（SuRE）方法的持续发展，以制造具有药用意义的大环，特别是环肽。通常，大环肽/肽模拟物是通过长线性前体的端到端环化制备的：这是一个困难且不可预测的过程。不需要的副反应，特别是二聚化过程，是主要问题；大环化反应通常在高稀释度下进行，以尽量减少这些问题，但很少完全避免，通常导致低收率，不切实际的工艺，特别是在大规模时。SuRE是一种完全避免端到端环化的替代策略，在York发表的工作中得到了验证，其中我们证明了环β -酮酯可以与线性酸氯偶联，并在保护基团裂解的情况下，在一个锅中进行环化和自发环扩张。环膨胀反应的设计是这样的，即启动装置中的功能在产品中被复制（黄色圈），因此相同的耦合/环膨胀序列可以重复：因此，通过将线性片段插入现有的环系统，可以有效地“生长”越来越大的环。迄今为止，工作主要集中在环β -酮酯与氨基酸和羟基酸的扩环。该项目的主要目标是通过开发新的SuRE反应体系来扩展SuRE反应工具箱，基于简单内酰胺的连续扩环成环肽，然后将这些产品用于医学导向应用。具体目标如下：a)利用N，N-苄基- fmoc保护的氨基酸氯化物作为线性片段，实现可控的连续扩环；在这种方法中，再生的nh -内酰胺作为一个手柄，允许进行环扩展。如果需要，n -苄基可以在合成结束时氢解裂解。b)另一种选择是，保护fmoc的初级氨基酸氯化物可用于生成具有两个新的nh -内酰胺基序的扩环内酰胺。这样的产物可以经过双环扩张产生含有四个内酰胺基团的大环，而大环又可以再次扩张（这次是通过四环扩张！），通过这种类型的指数增长，可能会提供含有8个氨基酸片段的高度复杂的环产物。该策略和“方法(a)”都代表了一种概念上的新方法，用于快速形成具有重要药用价值的“钉接肽”。c)使用环二肽（二酮哌嗪）作为起始材料，应该可以获得全肽大环；例如，四肽可以在一步中形成。此外，这些产品的额外扩展应该允许在一个步骤中产生更大的环。相对较小的环肽在药物发现方面具有很大的潜力，但它们特别难以通过传统的环化方法合成。合成的化合物将通过外部合作者和工业界的链接提交生物测定。d)如果时间允许，还计划证明SuRE可用于将治疗上重要的氨基酸序列安装到大环中；例如，缬氨酸-缬氨酸-半胱氨酸-酪氨酸序列，已被发现在已知的环肽HIF-1抑制剂中很重要。无数具有生物活性的环肽天然产物和药物制剂也是已知的，并且将选择展示所开发方法的目标；例如caspofunins类似物的合成。

Fundamentally, this project is based on the continued developed of the 'Successive Ring Expansion' (SuRE) method to make macrocycles of medicinal importance, especially cyclic peptides. Typically, macrocyclic peptides/peptide mimetics are prepared via the end-to-end cyclisation of a long linear precursor: a difficult and unpredictable process. Unwanted side reactions, especially dimerisation processes, are a major problem; macrocyclisation reactions are generally performed at high dilution to minimise such problems, but they are rarely avoided entirely, often resulting in low yielding, impractical processes, especially on large scale. SuRE is an alternative strategy in which end-to-end cyclisation is entirely avoided, validated in published work from York, in which we demonstrated that cyclic beta-keto esters can be coupled with linear acid chloride and upon protecting group cleavage, undergo cyclisation and spontaneous ring expansion in one-pot. The ring expansion reactions are designed such that the functionality present in the starter unit is replicated in the product (circled in yellow), therefore the same coupling/ring expansion sequence can be repeated: thus, rings of increasing size can effectively be 'grown', by inserting linear fragments into an existing ring system. To date, work has focused on the ring expansion of cyclic beta-keto esters with amino and hydroxy acids. The main goal of this project is to expand the SuRE reaction toolbox through the development new SuRE reaction systems, based on the successive ring expansion of simple lactams into cyclic peptides, and to then use these products in medicinally oriented applications. Specific goals are listed below: a) By utilising N,N-benzyl-Fmoc protected amino acid chlorides as linear fragments, controlled successive ring expansion should be achievable; in this method the regenerated NH-lactam serves as a handle to allow the ring expansion to be performed. The N-benzyl groups could be cleaved by hydrogenolysis at the end of the synthesis if required. b) Alternatively, primary Fmoc-protected amino acid chlorides could be used to generate ring expanded lactams with two new NH-lactam motifs. Such products could then undergo double ring expansion to generate macrocycles containing four lactam groups, which in turn could be expanded again (this time via a quadruple ring expansion!) potentially furnishing highly complex cyclic products containing 8 amino acid fragments, via this type of exponential growth remarkably quickly. Both this strategy and 'method (a)' represent a conceptually new approach for the rapid formation of medicinally important 'stapled peptides'.c) Fully peptidic macrocycles should be accessible using cyclic dipeptides (diketopiperazines) as starting materials; e.g. tetrapeptides may be formed in a single step. Furthermore, an additional expansion of these products should allow even larger rings to be generated in just one more step. Relatively small cyclic peptides have much potential in drug discovery, but they are particularly difficult to synthesise via conventional cyclisation methods. Synthesised compounds will be submitted for bioassay through links external collaborators and industry.d) If time allows, it is also planned to demonstrate that SuRE can be used to install therapeutically important amino acid sequences into macrocycles; e.g. the valine-valine-cysteine-tyrosine sequence, which has been found to be important in known cyclic peptide HIF-1 inhibitors. Countless biologically active cyclic peptide natural products and pharmaceutical agents are also known and targets that showcase the methods developed will be chosen; e.g. the synthesis of caspofungin analogues.