Chichibabin and IsoChichibabin Pyridinium Syntheses of Isodesmosine, Desmosine, and their Derivatives

Synthesis and applications of symmetric amino acid derivatives

Symmetric α-amino acid derivatives can be used for the synthesis of intermolecularly linked peptides such as dimer-type peptides, and modified peptides in which two amino acids are intramolecularly linked. They are also synthetic intermediates for the total synthesis of natural products and functional molecules. These symmetric amino acid derivatives must be prepared based on organic synthesis. It is necessary to develop an optimal synthetic strategy for constructing the target symmetric amino acid derivative. In this review, we will introduce strategies for synthesizing symmetric amino acid derivatives. Additionally, selected applications of these amino acids in the life sciences will be described.

Isotope-dilution LC-MS/MS analysis of the elastin crosslinkers desmosine and isodesmosine in acute cerebral stroke patients

Utilizing chemically synthesized an isotopically labeled internal standard, isodesmosine-13C3,15N1, an isotope-dilution LC-MS/MS method was established. Concentrations of desmosine and isodesmosine in plasma of acute cerebral stroke patients and healthy controls were determined. The concentration of desmosines was markedly higher in plasma from acute stroke patients compared with healthy controls. Desmosines are thus novel biomarkers for evaluating the extent of vascular injury after acute cerebral stroke.

IsoChichibabin desmosine-13C3,15N1 synthesis and quantitative LC-MS/MS analysis of desmosine and isodesmosine in human skin

Desmosine and isodesmosine are crosslinking amino acids of elastin, which is an essential component of the dermal extracellular matrix protein. Quantitative analysis of crosslinker desmosines in human skin dermis has not been fully achieved due to the insoluble nature of elastin protein. In the present study, chemical synthesis of isotopically labeled desmosine, desmosine-¹³C₃,¹⁵N₁, was carried out via isoChichibabin pyridinium synthesis starting from corresponding isotopically labeled amino acids. Isotope-dilution LC-MS/MS analysis of desmosine and isodesmosine utilizing synthetic desmosine-¹³C₃,¹⁵N₁ enabled the quantitative analysis of desmosines in human skin for the first time. Thus, ca. 1.43 μg of desmosines was detected from analysis of 1 mg of dry human skin.

Chichibabin/isoChichibabin pyridinium synthesis of ma'edamines C and D

Ma'edamines C and D were isolated from an Okinawan marine sponge and exhibited a unique tetrasubstituted pyridinium skeleton. The proposed biosynthetic pathway is similar to that of desmosine and isodesmosine, which are elastin-crosslinking amino acids. In this study, first total synthesis of ma'edamines C and D was achieved via Pr(OTf)₃-promoted Chichibabin/isoChichibabin pyridinium synthesis starting from the corresponding aldehydes and amine.

Chichibabin pyridinium synthesis via oxidative decarboxylation of photoexcited α-enamine acids

A visible light-induced decarboxylative Chichibabin pyridinium synthesis between α-amino acids and aldehydes was developed. When the in situ generated α-enamine acids were photoexcited, they were oxidized by aerobic oxygen to give radical cation species. After decarboxylation and further oxidation, the generated iminium undergoes Chichibabin cyclization to afford pyridiniums. This photochemical protocol enables the synthesis of various tetra-substituted pyridiniums and related natural products in one-step.

Preparation of isodesmosine-KLH conjugate for ELISA system

Chronic obstructive pulmonary disease (COPD) is a degenerative condition with limited diagnostic detection efficiency. Currently with no available cure, COPD is associated with irreversible elastic tissue degradation in lungs, which results in release of unusual amino acids, isodesmosine and desmosine. These biomarkers are potential key elements in enzyme-linked immunosorbent assay (ELISA), an analytical method, which can detect certain compounds including antigens and proteins in easy and affordable manner. In order to target a biomarker with ELISA, it is necessary to prepare its specific antibody, which can be achieved by immunization of host organism with appropriate antigen containing the biomarker. Although preparation of these types of conjugates has been published, desmosine and isodesmosine used by researchers are obtained from natural sources such as animal tissues. Here, we report the first synthetic preparation of isodesmosine and keyhole limpet hemocyanin (KLH) conjugate from commercially available chiral amino acids and carrier protein. Formation of the core pyridinium of isodesmosine was achieved through key reaction-Chichibabin pyridinium synthesis-to deliver a 1,2,3,5-tetrasubstituted pyridinium amino acid selectively. Further modifications involving KLH and maleimide linker provided the target conjugate, which could potentially invoke an immune response to produce anti-isodesmosine antibody for the ELISA system.