Usuki Toyonobu

This article introduces two topics regarding borderless natural product chemistry which has been conducted in our laboratory. The first theme presents the extraction and isolation of natural products from plant materials using ionic liquids that dissolve cellulose. Example of the study shows that shikimic acid was efficiently extracted from Ginkgo biloba leaves using [C 4mim] Cl. In the second topic, natural amino acid syntheses for clinical applications are shown. Desmosine and isodesmosine are tetrasubstituted pyridinium amino acids and are elastin crosslinkers as well as COPD biomarkers. The syntheses were achieved via palladium catalyzed cross-coupling reactions, or P (r OTf)3-promoted Chichibabin pyridinium synthesis.

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 ([C(2)mim][(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.

Desmosine is a crosslinking pyridinium amino acid of elastin, which is a useful biomarker for the diagnosis of chronic obstructive pulmonary disease (COPD) by LC–MS/MS analysis. We previously reported a synthesis of desmosine-d4, which is useful as an internal standard for quantitative LC–MS/MS analysis of desmosines, by deuterogenation of an alkyne group however, the isotopic purity of the desmosine-d4was only ca. 50%. The present report describes a new synthesis of desmosine-d4that improves the isotopic purity to ca. 90% by exchanging the protons of the amino groups to deuterium using deuterogenation.

Elastin is a vital extracellular matrix protein, which is known for providing elasticity in numerous tissues. It is formed by the self-assembly and subsequent crosslinking of elastin precursor, tropoelastin. Two tetrafunctional, pyridinium-based amino acids desmosine and isodesmosine are exclusively found in elastin and play an important role as crosslinkers. Structural elucidation of elastin has eluded scientists to date, owing to the highly cross-linked structure and insoluble nature. Therefore, in this study, we aimed to synthesize a desmosine-containing cyclic peptide as a partial elastin mimic, in order to eventually facilitate the elucidation of the crosslinking pattern of elastin by mass spectrometric analysis.

Monoalkynylpyridines were prepared via a Sonogashira cross-coupling reaction between monoiodopyridines and alkynes. Mild hydrogenation of the obtained monoalkynylpyridines was then conducted to produce the corresponding monoalkylpiperidines in moderate to excellent yields. The hydrogenation reaction was carried out under H2 (1 atm) in the presence of 10 wt% Pd/C (5 eq) in either AcOH or MeOH at room temperature. The present mild method is therefore useful for the quick and easy preparation of monoalkylpiperidines.

The essential oil components linalool, β-ionone, cis- and trans-linalool oxide pyranoid, and trans-linalool oxide furanoid, which are found in the flowers of Osmanthus fragrans var. aurantiacus, were efficiently extracted using a cellulosedissolving ionic liquid 1-ethyl-3-methylimidazolium methylphosphonate ([C2mim][(MeO)(H)PO2]) as an extraction solvent. Investigation of extraction time revealed that the ionic liquid contributed to the efficient extraction of these essential oils over a shorter extraction time. Scanning electron microscopy (SEM) and fluorescence microscopy observations of the flower petals confirmed the efficiency of the ionic liquid in this extraction process.

4-Methyl-5-pentylbenzene-1,3-diol (MPBD) is a secondary metabolite of SteelyA polyketide synthase, which controls cell aggregation and spore maturation of Dictyostelium discoideum. In this study, chemical synthesis of MPBD and its derivatives was achieved. Structure-activity relationship (SAR) studies for antimicrobial activities against Escherichia coli and Bacillus subtilis were also conducted. (C) 2016 Elsevier Ltd. All rights reserved.

A new lanostane triterpene was extracted from Ganoderma lucidum using cellulose-dissolving ionic liquids. The structure of the isolated compound was elucidated by spectroscopic analysis, including NMR, MS, and a modified Mosher's method. The newly isolated lanostane natural product was named ganoderic acid Σ.

Cnicin is a germacranolide sesquiterpene lactone that possesses potent inhibitory activity against the protozoan parasite Trypanosoma brucei, which causes human African trypanosomiasis (HAT). Although cnicin has an interesting structure and attractive biological activity, synthetic studies of cnicin have not yet been reported. This report describes the synthesis of the protected side chain carboxylic acid moiety at C8 of cnicin via two routes starting from L-ascorbic acid. In addition, esterification between the synthetic side chain and salonitenolide derivative, which can be achieved via hydrolysis of cnicin and protection of the primary alcohol, was conducted. Thus, a semi-synthesis of cnicin was achieved.

Isolated from the Jamaican cyanobacterium Lyngbya majuscula, the jamaicamides are unique, mixed polyketide-peptides reported to be sodium channel blockers. The polyketide moiety contains an (E)-chloroolefin, an undetermined methyl stereocenter (C9), and an (E)-olefin (C10-C11). Herein we report the stereo- and regioselective synthesis of the polyketide moiety of the jamaicamides via a Julia-Kocienski coupling as the key step. (C) 2015 Elsevier Ltd. All rights reserved.

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 cynaropicrin's deuterated derivative, cynaropicrin-d(4), by the replacement of the side chain of natural cynaropicrin. The synthesized cynaropicrin-d(4) 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. (C) 2015 Elsevier Ltd. All rights reserved.

Isodesmosine is a crosslinking pyridinium amino acid of elastin and is an attractive biomarker for the diagnosis of chronic obstructive pulmonary disease (COPD). In this paper, we describe the total synthesis of isodesmosine. The key features of this synthesis are stepwise and regioselective palladium-catalyzed Negishi and Sonogashira cross-coupling reactions for efficient introduction of amino acid segments on the pyridine ring.

Desmosine is a crosslinking pyridinium amino acid of elastin and is an attractive biomarker for the diagnosis of chronic obstructive pulmonary disease (COPD). Herein, we describe the total synthesis of natural desmosine and its deuterated derivatives. The synthesized deuterated derivatives could be used as internal standards for the development of an isotope-dilution liquid chromatography-mass spectrometry (LC-MS/MS) analytical method for the accurate determination of desmosine in clinical samples. The key features of our synthesis are stepwise chemo- and regioselective palladium-catalyzed Sonogashira and Negishi cross-coupling reactions for the efficient introduction of the amino acid side chains onto the pyridine core. (C) 2015 Elsevier Ltd. All rights reserved.

Desmosine, a COPD biomarker and elastin crosslinker, is a tetrasubstituted pyridinium amino acid. In this paper, the total synthesis of desmosine is described utilizing stepwise and regioselective palladium-catalyzed Sonogashira cross-coupling reactions of trihalopyridines and terminal alkynes as key steps. The 13-step synthesis starting from 4-hydroxypyridine was achieved in 11% overall yield.

A protocol for extracting the terpene trilactone bilobalide from Ginkgo biloba leaves using the cellulose-dissolving ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) was developed. Extraction with [C4mim]Cl/MeOH (1:1 w/w) at 80°C afforded bilobalide with a yield of 0.14% w/w, which was 1.4 times higher than that achieved using conventional MeOH at 80°C (0.098% w/w).

1,2,3,5-Tetrasubstituted pyridinium amino acid isodesmosine is a crosslinking amino acid of elastin and is an attractive biomarker for the diagnosis of chronic obstructive pulmonary disease (COPD). Herein, we report an application of the Chichibabin pyridine synthesis to the total synthesis of isodesmosine. Specifically, the appropriate protected lysine and the corresponding aldehyde were reacted using Pr(OTf)(3) in H2O/MeOH. (C) 2014 Elsevier Ltd. All rights reserved.

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.

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 alpha-methylene-gamma-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.

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. (C) 2013 Elsevier Ltd. All rights reserved.

The Negishi cross-coupling reaction of an organozinc derivative prepared from protected l-aspartic acid with monohalopyridines was improved by employing a combination catalyst of Pd-2(dba)(3) and P(2-furyl)(3) and removing an extra Zn from the organozinc reagent via centrifugation. The reactivity of halogenated pyridines (Cl, Br, I) with substituents at the C2, C3, and C4 positions of the pyridine ring was investigated, and it was found that the use of 4-iodopyridine as a substrate gave the best yield (90%) for the cross-coupling reaction.

Desmosine-CH2, an analog of the elastic tissue degradation biomarker desmosine, can be regarded as a potential internal standard for precise quantification of desmosines by LC-MS/MS. In this study, the chemical synthesis of desmosine-CH2 was completed in 22% overall yield in five steps. The LC-MS/MS analysis of desmosine-CH2 was also achieved.

A three-step synthesis of (R)-7-hydroxycarvone (1), which is anticipated to be a valuable building block for the versatile preparation of natural products, is described. Optimization of the reaction conditions for photooxygenation and migration of (S)-alpha-pinene 2, tetrapropylammonium perruthenate (TPAP) oxidation of the generated alcohol, and a subsequent ring-opening reaction in the presence of Cu(OTt)(2) led to the synthesis of 1 with good reproducibility. The desired product 1 was thus obtained in 46% yield over three steps. (C) 2013 Elsevier Ltd. All rights reserved.

Chronic obstructive pulmonary disease (COPD) is a respiratory disorder and is the fourth leading cause of death worldwide. Presently, there is a lack of effective medicines that can prevent progression of the disease, and thus survival rates cannot be improved. The development of biomarkers that can act as indicators of the severity of COPD and the level of patients' response to therapy would thus aid the drug discovery activities. Elastin fibers are a part of the extracellular matrix and are an essential structural component of the lungs, ligaments, skin, blood vessels, etc. Desmosine (1) and isodesmosine (2) are crosslinking amino acids of elastin. The irreversible degradation of lung elastin that occurs in COPD is known to give rise to these two amino acids, which can be measured in clinical samples by LC-MS. Therefore, 1 and 2 are useful as attractive biomarkers for both drug discovery and rapid diagnosis of COPD. In this study, total synthesis of COPD biomarkers 1 and 2 and the related amino acids are reported utilizing palladium-catalyzed cross-coupling reactions.

The jamaicamides, isolated in Jamaica from the cyanobacterium Lyngbya majuscula, are new mixed polyketide-peptides that are known to be sodium channel blockers. The polyketide moiety contains an (E)-vinyl chloride, an undetermined methyl stereocenter (C9), and an (E)-olefin. Herein, we report the synthesis of the (E)-olefin moiety of the polyketide of the jamaicamides utilizing a KocienskiJulia coupling. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications (R) to view the free supplemental file. GRAPHICAL ABSTRACT

The first total synthesis of the diaiylheptanoid acerogenins E and K, isolated from Acer nikoense MAXIM., is described. Formation of the 13-membered m,m-cyclophane skeleton was successfully achieved on the basis of a domino process involving a Miyaura arylborylation intramolecular Suzuki reaction. The cyclization precursor was prepared via a Wittig reaction and Claisen Schmidt condensation, which proceeded in moderate yields. The total synthesis of acerogenin G and centrolobol was also achieved from a common synthetic intermediate. (C) 2013 Elsevier Ltd. All rights reserved.

Neodesmosine, isolated from the hydrolysate of bovine ligamentum nuchae, is a crosslinking pyridinium amino acid of elastin. In this study, the first total synthesis of neodesmosine is reported via a Negishi cross-coupling reaction between 3,5-dihalogenated pyridines and the corresponding iodo amino acid.

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. © 2013 Elsevier Inc. All rights reserved.

Magnolignan, 2,2'-dihydroxy-5,5'-dipropyl-biphenyl (1), is a down-regulator of melanin synthesis that inhibits the maturation of tyrosinase. In this study, a concise total synthesis of 1 was achieved in five steps with 50% overall yield starting from commercially available trans-anethole (2) via a Suzuki-Miyaura reaction.

Desmopyridine, isolated from the acid hydrolysates of bovine ligamentum nuchae, is an elastin crosslinker and an amino acid that has a 3,4,5-trisubstituted pyridine skeleton. Herein we report the first total synthesis of (+)-desmopyridine in 10% yield over six steps starting from 4-aminopyridine via chemo- and regioselective palladium-catalyzed Sonogashira and Negishi cross-coupling reactions. (C) 2012 Elsevier Ltd. All rights reserved.

Desmosine, a crosslinking pyridinium amino acid of elastin, is an attractive biomarker for the diagnosis of chronic obstructive pulmonary disease (COPD). In this study, the total synthesis of (+)-desmosine is reported utilizing chemo- and regioselective Sonogashira and Negishi cross-coupling reactions in 15% yield over six steps. (C) 2012 Elsevier Ltd. All rights reserved.

Abstract Circular dichroism (CD) spectroscopy has been a powerful technique in the structural analysis of various chiral supramolecular systems. In order to obtain correct structural information it is essential to understand the basic concepts of CD, to optimize the measurement condition, and to properly interpret the data. This chapter addresses the following topics in order for the readers to use CD spectroscopy more efficiently: (i) the fundamental principles of CD spectroscopy and the technical point of the measurements; (ii) the exciton chirality method and its use in the configurational and conformational analysis of supermolecules; (iii) the introduction of basic concepts of induced CD; and (iv) the recent developments of computational simulation of CD spectra. We show that these basic concepts are applicable to the interpretation of CD data of further complicated supramolecular systems, by showing examples of a broad range of chiral supermolecules such as host‐guest systems, mechanically interlocked molecules, molecular machines, foldamer, polymers, and self‐assembled molecules. This chapter also briefly introduces the applications of a newly emerged CD (vibrational circular dichroism (VCD) spectroscopy) to supermolecules.

Introduction - Terpene trilactones (TTLs), unique components of Ginkgo biloba extracts, are believed to play important roles in the biological activity of these materials. The investigation of seasonal and gender-related variations in the natural content of TTLs in the leaves is a challenging problem that must be addressed in order to establish more efficient extraction/isolation protocols for TTLs. Objective - The aims of this work were (i) to modify the extraction/isolation protocols of TTLs from G. biloba leaves by means of boiling and filtration procedures, and (ii) to investigate seasonal and gender-related variations in the TTL content of the leaves via (1)H-NMR analysis. Methodology - When extracting TTLs from G. biloba leaves, procedures for boiling and filtration were improved in this work. Moreover, quantitative (1)H-NMR analysis using DMF as a reference was performed and correlated to the colour (green/yellow) and gender (male/female) variations in the natural compositions of TTLs in the leaves. Results - Extraction procedures were modified to include boiling in ethyl acetate and filtration was achieved with celite. (1)H-NMR analysis of TTLs suggested that green female leaves contained the largest amount of TTLs, while no TTLs were present in yellow male leaves. Conclusion - The present results provide a method for quickly supplying laboratory-scale quantities of TTLs from natural sources to enable the study of their structure-activity relationships. Copyright (C) 2011 John Wiley & Sons, Ltd.

Desmosine, a crosslinking amino acid of elastin, is an attractive biomarker for diagnosis of chronic obstructive pulmonary disease (COPD). In this study, the first total synthesis of (+)-desmosine was achieved in 11% overall yield in 13 steps utilizing stepwise and regioselective Sonogashira cross-coupling reactions.

Bilobalide, a unique constituent of Ginkgo biloba, has been reported to potentiate population spikes in hippocampal CA1 pyramidal cells and to protect the brain against cell death. In this study, the effects of bilobalide on synaptic transmission and its plasticity in rat hippocampal subfields were electrophysiologically investigated. Bilobalide (50 mu M) significantly potentiated the input-output relationship at Schaffer collateral (SC)-CA1 synapses but not at medial perforant path (MPP)-dentate gyrus (DG), lateral perforant path (LPP)-DG, or mossy fiber (MF)-CA3 synapses. Facilitative effects of bilobalide on synaptic plasticity were only observed at MPP-DG synapses, in which the induction of long-term depression was blocked in the presence of bilobalide. However, no effect on synaptic plasticity was observed at SC-CA1 synapses. These results suggest that bilobalide has differential effects on synaptic efficacy in each hippocampal subfield.

The jamaicamides, isolated from cyanobacterium Lyngbya majuscula in Jamaica, are unique mixed polyketide-peptides that are reported to be blockers of the sodium channels. The peptide moiety contains a pyrrolinone ring and a beta-methoxy enone functionality. Herein, we report the stereoselective synthesis of the N-(Boc)(2)-protected peptide moiety of the jamaicamides by utilizing Meldrum's acid starting from L-alanine and N-Boc-beta-alanine. (C) 2011 Elsevier Ltd. All rights reserved.

The efficient synthesis of four benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-omega-iodoalkanoates {benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-3-iodopropanoate, benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-4-iodobutanoate, benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-5-iodopentanoate, benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-6-iodohexanoate) from natural or protected L-amino acids is described. (C) 2011 Elsevier Ltd. All rights reserved.

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.

Shikimic acid, the starting material in the commercial synthesis of oseltamivir phosphate (Tamiflu (R)), was efficiently extracted and isolated from Ginkgo biloba leaves utilizing the ionic liquid 1-butyl-3-methylimidazolium chloride ([bmim]Cl), which dissolves cellulose.