Division of Biological Chemistry and Drug Discovery, School of Life Sciences , University of Dundee , James Black Centre, Dow Street , Dundee DD1 5EH , Scotland, U.K.
Department of Chemistry , University of Aberdeen , Meston Walk , Aberdeen AB24 3UE , Scotland, U.K.
J Am Chem Soc. 2018 Jul 25;140(29):9299-9313. doi: 10.1021/jacs.8b05807. Epub 2018 Jul 12.
Hydroxylation and fluorination of proline alters the pyrrolidine ring pucker and the trans:cis amide bond ratio in a stereochemistry-dependent fashion, affecting molecular recognition of proline-containing molecules by biological systems. While hydroxyprolines and fluoroprolines are common motifs in medicinal and biological chemistry, the synthesis and molecular properties of prolines containing both modifications, i.e., fluoro-hydroxyprolines, have not been described. Here we present a practical and facile synthesis of all four diastereoisomers of 3-fluoro-4-hydroxyprolines (F-Hyps), starting from readily available 4-oxo-l-proline derivatives. Small-molecule X-ray crystallography, NMR spectroscopy, and quantum mechanical calculations are consistent with fluorination at C having negligible effects on the hydrogen bond donor capacity of the C hydroxyl, but inverting the natural preference of Hyp from C-exo to C-endo pucker. In spite of this, F-Hyps still bind to the von Hippel-Lindau (VHL) E3 ligase, which naturally recognizes C-exo Hyp in a stereoselective fashion. Co-crystal structures and electrostatic potential calculations support and rationalize the observed preferential recognition for (3 R,4 S)-F-Hyp over the corresponding (3 S,4 S) epimer by VHL. We show that (3 R,4 S)-F-Hyp provides bioisosteric Hyp substitution in both hypoxia-inducible factor 1 alpha (HIF-1α) substrate peptides and peptidomimetic ligands that form part of PROTAC (proteolysis targeting chimera) conjugates for targeted protein degradation. Despite a weakened affinity, Hyp substitution with (3 S,4 S)-F-Hyp within the PROTAC MZ1 led to Brd4-selective cellular degradation at concentrations >100-fold lower than the binary K for VHL. We anticipate that the disclosed chemistry of 3-fluoro-4-hydroxyprolines and their application as VHL ligands for targeted protein degradation will be of wide interest to medicinal organic chemists, chemical biologists, and drug discoverers alike.
顺式酰胺键的比例，影响生物系统对含脯氨酸分子的分子识别。虽然羟脯氨酸和氟脯氨酸是药物和生物化学中的常见结构单元，但同时含有这两种修饰的脯氨酸，即氟羟脯氨酸的合成和分子性质尚未被描述。在这里，我们从易得的 4-氧代-L-脯氨酸衍生物出发，提出了一种实用且简便的合成所有四种立体异构体 3-氟-4-羟基脯氨酸（F-Hyps）的方法。小分子 X 射线晶体学、NMR 光谱和量子力学计算表明，氟原子在 C 位的取代对 C 羟基的氢键供体能力几乎没有影响，但将 Hyp 的天然偏好从 C-外消旋翻转到 C-内消旋构象。尽管如此，F-Hyps 仍然与 von Hippel-Lindau（VHL）E3 连接酶结合，后者以立体选择性的方式自然识别 C-外消旋 Hyp。共晶结构和静电势计算支持并解释了 VHL 对（3R,4S）-F-Hyp 的优先识别，而不是相应的（3S,4S）差向异构体。我们表明，（3R,4S）-F-Hyp 在缺氧诱导因子 1α（HIF-1α）底物肽和形成 PROTAC（蛋白酶体靶向嵌合体）缀合物一部分的肽模拟配体中提供了与 Hyp 生物等排的取代，用于靶向蛋白质降解。尽管亲和力减弱，但在 PROTAC MZ1 中用（3S,4S）-F-Hyp 取代 Hyp 导致 Brd4 的选择性细胞降解，其浓度比 VHL 的二元 K 低 100 多倍。我们预计，所公开的 3-氟-4-羟基脯氨酸化学及其作为 VHL 配体用于靶向蛋白质降解的应用将引起药物有机化学家、化学生物学家和药物发现者的广泛关注。
