Soto-Martínez Diana M, Clements Garrett D, Díaz John E, Becher Joy, Reynolds Robert C, Ochsenbauer Christina, Snowden Timothy S
Department of Chemistry and Biochemistry, The University of Alabama 250 Hackberry Lane Tuscaloosa AL 35487 USA
Department of Medicine, Division of Hematology and Oncology, University of Alabama at Birmingham Birmingham AL 35294 USA.
RSC Adv. 2024 May 28;14(24):17077-17090. doi: 10.1039/d4ra01974a. eCollection 2024 May 22.
The von Hippel-Lindau (VHL) protein serves as the substrate recognition subunit of the multi-subunit Cullin-2 RING E3 ubiquitin ligase (CRL2), which regulates intracellular concentrations of hypoxia inducible factors (HIFs) through a ubiquitin proteasome system (UPS) cascade. Strategic recruitment of CRL2 by bi- or trifunctional targeted protein degraders (, PROTACs®) offers the prospect of promoting aberrant polyubiquitination and ensuing proteasomal degradation of disease-related proteins. Non-peptidic, l-hydroxyproline-bearing VHL ligands such as VH032 (1) and its chiral benzylic amine analog Me-VH032 (2), are functional components of targeted protein degraders commonly employed for this purpose. Herein, we compare two approaches for the preparation of 1 and 2 primarily highlighting performance differences between Pd(OAc) and Pd-PEPPSI-IPr for the key C-H arylation of 4-methylthiazole. Results from this comparison prompted the development of a unified, five-step route for the preparation of either VH032 (1) or Me-VH032 (2) in multigram quantities, resulting in yields of 56% and 61% for 1 and 2, respectively. Application of -Boc-l-4-hydroxyproline rather than -butoxycarbonyl to shield the benzylic amine during the coupling step enhances step economy. Additionally, we identified previously undisclosed minor byproducts generated during arylation steps along with observations from amine deprotection and amidation reaction steps that may prove helpful not only for the preparation of 1 and 2, but for other VHL recruiting ligands, as well.
冯·希佩尔-林道（VHL）蛋白作为多亚基Cullin-2 RING E3泛素连接酶（CRL2）的底物识别亚基，通过泛素蛋白酶体系统（UPS）级联反应调节细胞内缺氧诱导因子（HIFs）的浓度。双功能或三功能靶向蛋白降解剂（如PROTACs®）对CRL2的策略性募集为促进异常多聚泛素化以及随后疾病相关蛋白的蛋白酶体降解提供了前景。非肽类、含l-羟基脯氨酸的VHL配体，如VH032（1）及其手性苄胺类似物Me-VH032（2），是常用于此目的的靶向蛋白降解剂的功能成分。在此，我们比较了两种制备1和2的方法，主要突出了Pd（OAc）和Pd-PEPPSI-IPr在4-甲基噻唑关键C-H芳基化反应中的性能差异。该比较结果促使我们开发了一种统一的五步路线，用于多克量制备VH032（1）或Me-VH032（2），1和2的产率分别为56%和61%。在偶联步骤中应用-Boc-l-4-羟基脯氨酸而非-丁氧羰基来保护苄胺可提高步骤经济性。此外，我们鉴定出了芳基化步骤中产生的先前未公开的次要副产物，以及胺脱保护和酰胺化反应步骤中的观察结果，这些不仅可能有助于1和2的制备，也可能有助于其他VHL募集配体的制备。
