Toyonobu Usuki

Stable deuterium internal standard for the isotope-dilution LC–MS/MS analysis of elastin degradation

Chemical synthesis of the deuterium isotope desmosine-d4 has been achieved. This isotopic compound possesses all four deuterium atoms at the alkanyl carbons of the alkyl amino acid substitution in the desmosine molecule and is stable toward acid hydrolysis; this is required in the measurement of two crosslinking molecules, desmosine and isodesmosine, as biomarkers of elastic tissue degradation. The degradation of elastin occurs in several widely prevalent diseases. The synthesized desmosine-d₄ is used as the internal standard to develop an accurate and sensitive isotope-dilution liquid chromatography-tandem mass spectrometry analysis, which can serve as a generalized method for an accurate analysis of desmosine and isodesmosine as biomarkers in many types of biological tissues involving elastin degradation.

Biomimetic Chichibabin pyridine synthesis of the COPD biomarkers and elastin cross-linkers isodesmosine and desmosine.

The tetrasubstituted pyridinium amino acids isodesmosine and desmosine are cross-linkers of elastin and are attractive biomarkers for the diagnosis of chronic obstructive pulmonary disease (COPD). In this study, the biomimetic total synthesis of isodesmosine and desmosine via a lanthanide-promoted Chichibabin pyridine synthesis using the corresponding aldehyde and amine hydrochloride is reported.

Critical Importance of the Nine-Membered F Ring of Ciguatoxin for Potent Bioactivity: Total Synthesis and Biological Evaluation of F-Ring-Modified Analogues†

are made up of a single carbon chain locked into a ladderlike structure with a length of 3 nm. The striking regularity with which the oxygen atoms bridge the polycyclic framework is a remarkable feature of these molecules. The cyclic ethers, with sizes ranging from fiveto nine-membered rings, all fuse in a trans/syn/trans fashion. Ciguatoxins (1, Scheme 1) and brevetoxins (2 and 3) have attracted intense interest from biologists and chemists alike because of their potent neurotoxicity and their association with the catastrophic effects of food poisoning and redtide phenomena. Ciguatoxins were identified as the principle toxins in the widespread seafood poisoning known as ciguatera. The toxins generated by the dinoflagellate Gambierdiscus toxicus are transferred through the aquatic food chain, and ingestion of ciguateric fish by humans leads to neurological, gastrointestinal, and cardiovascular disorders. On the other hand, brevetoxins are potent ichthyotoxins, and have been isolated from the dinoflagellate Karenia breve. Red tides, which are caused by blooms of Karenia breve, have killed great numbers of fish and caused intoxication in humans. These toxins exert their toxicity by binding to the voltagesensitive sodium channels (VSSC) of excitable membranes, causing them to open, and thereby allowing influx of sodium ions. The specific binding site shared by ciguatoxins and brevetoxins was designated as site 5. Interestingly, more structurally complex ciguatoxins are known to possess both a higher binding affinity to site 5 and more potent toxicities than brevetoxins. The extremely limited supply of ciguatoxins from the natural sources has prevented studies on structure– activity relationships (SARs), which would help in understanding the structural requirements necessary for this highly specific ligand–receptor interaction. Thus, a synthetic supply of ciguatoxins is urgently needed. Recently, we achieved the first total synthesis of three members of the ciguatoxin family, namely CTX1B, CTX3C, and 51-hydroxyCTX3C (1), based on a unified synthetic strategy. These routes allowed us to prepare new fully synthetic analogues of ciguatoxins for detailed SAR studies. Here we report the total synthesis and biological evaluation of F-ring-modified analogues of 1. Scheme 2 illustrates the last stage of our total synthesis of 51-hydroxyCTX3C (1), one of the most toxic congeners of the ciguatoxins. The comparably complex left ABCDE and right HIJKLM wings were coupled through O,S-acetal formation. The FG ring was then constructed in a stepwise manner: radical cyclization of 5 generated the seven-membered G ring of 6, and ring-closing olefin metathesis (RCM) built the nine-membered F ring (7!8). Final removal of the 2-naphthylmethyl (NAP) groups from 8 afforded 1. This synthetic scheme offered a unique opporScheme 1. Structures of ciguatoxin 51-hydroxyCTX3C and brevetoxins.

Structure-Activity Relationship Study of Sesquiterpene Lactones and Their Semi-Synthetic Amino Derivatives as Potential Antitrypanosomal Products

Sesquiterpene lactones (STLs) are natural products that have potent antitrypanosomal activity in vitro and, in the case of cynaropicrin, also reduce parasitemia in the murine model of trypanosomiasis. To explore their structure-antitrypanosomal activity relationships, a set of 34 natural and semi-synthetic STLs and amino-STLs was tested in vitro against T. b. rhodesiense (which causes East African sleeping sickness) and mammalian cancer cells (rat bone myoblast L6 cells). It was found that the α-methylene-γ-lactone moiety is necessary for both antitrypanosomal effects and cytotoxicity. Antitrypanosomal selectivity is facilitated by 2-(hydroxymethyl)acrylate or 3,4-dihydroxy-2-methylenebutylate side chains, and by the presence of cyclopentenone rings. Semi-synthetic STL amines with morpholino and dimethylamino groups showed improved in vitro activity over the native STLs. The dimethylamino derivative of cynaropicrin was prepared and tested orally in the T. b. rhodesiense acute mouse model, where it showed reduced toxicity over cynaropicrin, but also lost antitrypanosomal activity.

Antitrypanosomal structure–activity-relationship study of synthetic cynaropicrin derivatives

Cynaropicrin is a guaianolide sesquiterpene lactone with a 5-7-5 tricyclic skeleton, four exo-olefins, and two hydroxyl groups. Recently, it was found that the compound is a potent in vitro and in vivo inhibitor of the protozoan parasite Trypanosoma brucei, which causes human African trypanosomiasis (HAT; sleeping sickness). In this Letter, chemical derivatization of cynaropicrin and the structure-activity-relationship (SAR) study against T. brucei is described.

Synthesis and biological evaluation of bilobol and adipostatin A

Concise total synthesis of bilobol 5-pentadecenylresorcinol (1), isolated from Gingko biloba fruits, has been achieved in 10 steps with 51% overall yield from 3,5-dihydroxybenzoic acid (3). Adipostatin A (2), isolated from the fruits as well as from Streptomyces cyaneus 2299-SV1, has also been synthesized in two steps from methylated bilobol (10). The structure–activity relationship study of synthetic products was described by means of cytotoxic assay against human KB carcinoma cell lines.

Direct Observation of ESR Spectra of Bicyclic Nine-Membered Enediynes at Ambient Temperature

The ESR spectra for synthetic bicyclo[7.3.0]epoxydodecadienediynes in solution at room temperature are steady. These spectra originate from the Masamune-Bergman cyclization of bicyclo[7.3.0]epoxydodecadienediynes to p-benzyne biradicals and the equilibrium between the two forms. Comparison of the ESR spectra of the unlabeled and 13 C-labeled nine-membered enediynes indicated that the spectra are not directly due to the p-benzyne biradicals but rather to more stable secondary radical intermediates.

[13C3,15N1]-labeled isodesmosine: A potential internal standard for LC–MS/MS analysis of desmosines in elastin degradation

Isodesmosine and desmosine are crosslinking amino acids that are present only in elastin. They are useful biomarkers for the degradation of elastin, which occurs during the progression of chronic obstructive pulmonary disease (COPD) and related diseases. This Letter describes the synthesis of [(13)C3,(15)N1]-labeled isodesmosine, using Chichibabin pyridine synthesis as a key reaction. The labeled isodesmosine is a potential internal standard for the quantitative LC-MS/MS analysis of desmosines in elastin degradation.

Improved Extraction Yield of Citral from Lemon Myrtle Using a Cellulose-Dissolving Ionic Liquid

Lemon myrtle is the richest natural source of citral, which has potential medicinal applications. In this study, citral was extracted from lemon myrtle using cellulose-dissolving ionic liquids (ILs), 1-ethyl-3-methylimidazolium methylphosphonate ([C2mim][(MeO)(H)PO2]), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium chloride ([DEME]Cl), and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium 2-methoxyacetate ([DEME][MOAc]). The extraction yield of citral obtained using ILs was up to 2.1 times higher than that obtained using ethanol. The ILs could be recycled and reused nine times for the extraction of citral. The present method provides a greener process when compared with conventional approaches and may be applicable for the extraction of other natural products.

Synthesis of cynaropicrin-d4

Cynaropicrin is a guaianolide sesquiterpene lactone, which has potent in vitro and in vivo inhibitory activity against Trypanosoma brucei, the protozoan parasite that causes human African trypanosomiasis (HAT; sleeping sickness). Herein, we describe the synthesis of cynaropicrins deuterated derivative, cynaropicrin-d4, by the replacement of the side chain of natural cynaropicrin. The synthesized cynaropicrin-d4 could be employed as an internal standard for liquid chromatography-mass spectrometry (LC-MS) analysis, in the pharmacokinetic study of cynaropicrin. This could potentially advance the study of this therapeutic lead.