A SuRE way to synthesise macrocyclic peptides

从根本上说，该项目是基于“连续扩环”（SuRE）方法的持续发展，以制造具有医学重要性的大环化合物，特别是环肽。通常，大环肽/肽模拟物通过长线性前体的端对端环化来制备：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，是一个主要问题;大环化反应通常在高稀释度下进行以最小化这些问题，但它们很少完全避免，通常导致低产率，不切实际的过程，特别是在大规模上。SuRE是一种完全避免端到端环化的替代策略，在约克发表的工作中得到了验证，其中我们证明了环状β-酮酯可以与线性酰氯偶联，并且在保护基断裂后，进行环化和自发环化。一锅法扩环。扩环反应被设计成使得起始单元中存在的官能度在产物中复制（黄色圈出），因此可以重复相同的偶联/扩环序列：因此，通过将线性片段插入现有的环系统中，可以有效地“生长”尺寸增加的环。迄今为止，工作重点是环状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反应系统来扩展SuRE反应工具箱，该系统基于简单内酰胺连续扩环为环肽，然后将这些产品用于医学应用。具体目标如下所列：a）通过利用N，N-苄基-Fmoc保护的氨基酸氯化物作为线性片段，应可实现受控的连续扩环;在该方法中，再生的NH-内酰胺用作允许进行扩环的手柄。如果需要，N-苄基可以在合成结束时通过氢解裂解。B）或者，可使用伯Fmoc保护的氨基酸氯化物来产生具有两个新NH-内酰胺基序的扩环内酰胺。这样的产物然后可以经历双环膨胀以生成含有四个内酰胺基团的大环，其又可以再次膨胀（这次通过四重环膨胀！）通过这种类型的指数增长，可能非常快速地提供含有8个氨基酸片段的高度复杂的环状产物。这种策略和“方法（a）”都代表了快速形成医学上重要的“钉合肽”的概念上的新方法。c）使用环状二肽（二酮哌嗪）作为起始材料应该可以获得全肽大环化合物;例如四肽可以在单个步骤中形成。此外，这些产品的额外扩展应该允许在多一个步骤中生成更大的环。相对小的环肽在药物发现中具有很大的潜力，但它们特别难以通过常规环化方法合成。合成的化合物将通过外部合作者和行业的链接提交进行生物测定。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，已发现在已知的环肽HIF-1抑制剂中重要的缬氨酸-缬氨酸-半胱氨酸-酪氨酸序列。无数具有生物活性的环肽天然产物和药剂也是已知的，并且将选择展示所开发的方法的目标;例如，卡泊芬净类似物的合成。

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.