We herein report an improved synthetic pathway to 5-thioxo-L-proline (2) (using R,S nomenclature, the L form here possesses the S configuration). Compound 2 is synthesized from naturally occurring 5-oxo-L-proline (1) at room temperature with 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (3) (Lawesson′s reagent, LR). The synthesis is an improved version of our previously published method. The optical purity of 2 has been proven by thin-layer chromatography based on chiral ligand exchange. The synthesis of N-acyl and S-alkyl derivatives of 5-thioxo-L-proline (Top-OH), 5-thioxo-L-proline methyl ester (Top-OCH₃), and the pseudodipeptide Boc-L-Phe-Top-OCH₃ is also described.

中文翻译：

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氨基酸和肽的研究，改进了5-硫代-L-脯氨酸的合成方法，以及一些N-酰基和S-烷基衍生物作为构建肽的基本组成部分13

我们在本文中报道了5-硫代-L-脯氨酸（2）的改进的合成途径（使用R，S命名法，此处的L形式具有S构型）。化合物2是在室温下由天然存在的5-氧代-L-脯氨酸（1）与2,4-双（4-甲氧基苯基）-1,3,2,4-二硫代二膦烷2,4-二硫化物（3）（ Lawesson试剂，LR）。该综合是我们以前发布的方法的改进版本。通过基于手性配体交换的薄层色谱法已经证明了2的光学纯度。N-酰基和S的合成还描述了5-硫代-L-脯氨酸（Top-OH），5-硫代-L-脯氨酸甲酯（Top-OCH ₃）和假二肽Boc-L-Phe-Top-OCH _3的-烷基衍生物。