Synthesis of diastereomerically pure Lys(N^ε‐lipoyl) building blocks and their use in Fmoc/tBu solid phase synthesis of lipoyl‐containing peptides for diagnosis of primary biliary cirrhosis

Abstract

Primary Biliary Cirrhosis is an immune-mediated disease in which one of the epitopes recognized by antimitochondrial autoantibodies is a lipoylated fragment of the PDC-E2 protein. Accordingly, the synthesis of lipoylated peptides as diagnostic tools is a relevant target. Up to now, the proper tools for the introduction of lipoylation on building blocks to be used in Fmoc/tBu solid phase peptide synthesis (SPPS) are lacking, and the role of chirality in lipoylation remains poorly studied. In this paper, we present the synthesis of lipoylated lysine derivatives as pure diastereomeric building blocks suitable for Fmoc/tBu SPPS and their introduction in relevant peptide sequences to possibly serve as synthetic probes for the development of novel diagnostic tools for this disease. The optimization of the synthesis of lipoylated building blocks derived from racemic, (R)-, and (S)-α-lipoic acid is described. Synthesis of peptide probes incorporating lipoylation is described. An insight regarding the cleavage of lipoylated peptides is given, as well as a method to oxidize or reduce the 1,2-dithiolane ring of the lipoyl moiety directly on the peptide without any subsequent purification.

A Photochromic Azobenzene Peptidomimetic of a β-Turn Model Peptide Structure as a Conformational Switch

“…The resin used was a Fmoc-Lys(Boc)-Wang (loading 0.24 mmol/g). Modified amino acids were introduced using the synthesized protected building-blocks suitable for Fmoc/tBu SPPS (Paolini et al, 2007; Rentier et al, 2015). Coupling was performed with the azobenzene amino acid AMPB (2.5 eq), HATU as activator (2.5 eq), and DIPEA (3.5 eq) for 30 min at room temperature.…”

Role of Lipoylation of the Immunodominant Epitope of Pyruvate Dehydrogenase Complex: Toward a Peptide-Based Diagnostic Assay for Primary Biliary Cirrhosis

“…This method, based on a building block approach, was reported elsewhere. 15 Once established the possibility to prepare unequivocally lipoylated peptides, we realized with preliminary immunological assays that our target sequence, i.e. [Lipoamide-…”

“…15 Briefly, both enantiomers of α-lipoic acid were coupled to the side-chain of Table 1. Immunological studies.…”

Epitope mapping of anti‐myelin oligodendrocyte glycoprotein (MOG) antibodies in a mouse model of multiple sclerosis: microwave‐assisted synthesis of the peptide antigens and ELISA screening

“…Next, we decided to split the C‐terminal 56–117 in three 20‐mer portions and to analyze separately the residual N‐terminal fragment, MOG(1–34). As peptide 6a displayed solubility issues, we decided to enhance the solubility of the sequence adding a C‐terminal 4‐Lys tag (peptide 6b ), as previously reported . Although the synthesis of the MOG peptide fragments 2–6b was not expected to be particularly demanding, we decided to use an optimized process for SPPS using MW irradiation combined with the Fmoc/tBu strategy.…”