ABSTRACT
Enantioselective total synthesis of the aglycone of burnettramic acid A, an antifungal pyrrolizidinedione with a terminally mannosylated long acyl chain produced by Aspergillus fungi, has been achieved from a known carboxylic acid by a 14-step sequence. The key steps include 2 types of asymmetric alkylation, coupling of an acetylide intermediate with (S)-epichlorohydrin to provide an acetylenic epoxide in 1 pot, and the Birch reduction to effect desulfonylation, semi-reduction of triple bond, and debenzylation in a concurrent manner. Good agreement of the synthetic aglycone with naturally occurring one in 1H and 13C nuclear magnetic resonance (NMR) spectra, coupled with previously reported unambiguous stereochemical assignment of the sugar moiety, has confirmed the structure of burnettramic acid A.
Subject(s)
Stereoisomerism , AlkylationABSTRACT
The total synthesis of the antibiotic amycolamicin with a hybrid molecular architecture composed of five ring systems, which exhibits potent antibacterial activity against a wide range of drug-resistant bacteria, has been achieved in a convergent manner. A protecting-group-free intramolecular Diels-Alder reaction of a hydroxy tetraenal intermediate promoted by two equivalents of Et2AlCl, which proceeds highly diastereoselectively via an endo-equatorial transition state, has been utilized to construct the trans-decalin moiety of the molecule. The full structure of amycolamicin was assembled by a completely stereoconvergent N-acylation of a northern N-glycoside unit (α-anomer/ß-anomer = 1:1.1) with a southern ß-keto thioester segment followed by installation of the central tetramic acid moiety.
Subject(s)
Anti-Bacterial Agents , Pyrroles , Anti-Bacterial Agents/chemistry , Glucosides/chemistry , Molecular Structure , Pyrroles/chemistry , StereoisomerismABSTRACT
An enantioselective total synthesis of sporothriolide, a bioactive furofurandione-type fungal metabolite, has been achieved in a 21% overall yield from a commercially available ß,γ-unsaturated carboxylic acid via seven steps. The key steps of this synthesis include a highly diastereoselective Michael addition of a chiral oxazolidinone derivative to a nitro olefin, the exploitation of an aromatic ring as a masked carboxylic acid functionality, and the base-promoted elimination of nitrous acid to install the α-methylene lactone unit of sporothriolide in the final step.
Subject(s)
Alkenes , Furans , Carboxylic Acids , StereoisomerismABSTRACT
The N-acyl amycolose moiety incorporated in amycolamicin, a broad-spectrum antibacterial natural product produced by soil actinomycetes, and its two anomeric methyl glycosides have been synthesized enantioselectively each in 12 steps from a known methyl ( R)-lactate derivative by exploiting a diastereoselective nucleophilic addition of a p-methoxybenzyloxy-substituted vinyllithium reagent to an α,ß-bisalkoxy ketone intermediate to provide the corresponding tertiary alcohol as a single diastereomer. The three sugar derivatives are known as cytotoxic degradation products of amycolamicin.
ABSTRACT
Understanding of lipid oxidation mechanisms (e.g., auto-oxidation and photo-oxidation) in foods and cosmetics is deemed essential to maintain the quality of such products. In this study, the oxidation mechanisms in foods and cosmetics were evaluated through analysis of linoleic acid hydroperoxide (LAOOH) and linoleic acid ethyl ester hydroperoxide (ELAOOH) isomers. Based on our previous method for analysis of LAOOH isomers, in this study, we developed a new HPLC-MS/MS method that enables analysis of ELAOOH isomers. The HPLC-MS/MS methods to analyze LAOOH and ELOOH isomers were applied to food (liquor) and cosmetic (skin cream) samples. As a result, LAOOH and ELAOOH isomers specific to photo-oxidation, and ELAOOH isomers characteristic to auto-oxidation were detected in some marketed liquor samples, suggesting that lipid oxidation of marketed liquor proceeds by both photo- and auto-oxidation during the manufacturing process and/or sales. In contrast, because only LAOOH and ELAOOH isomers specific to auto-oxidation were detected in skin cream stored under dark at different temperatures (-5 °C-40 °C) for different periods (2-15 months), auto-oxidation was considered to be the major oxidation mechanism in such samples. Therefore, our HPLC-MS/MS methods appear to be powerful tools to elucidate lipid oxidation mechanisms in food and cosmetic products.
Subject(s)
Beverages/analysis , Cosmetics/analysis , Linoleic Acids/analysis , Lipid Metabolism , Lipid Peroxides/analysis , Chromatography, High Pressure Liquid/methods , Cosmetics/chemistry , Feasibility Studies , Isomerism , Linoleic Acids/chemistry , Linoleic Acids/metabolism , Lipid Peroxides/chemistry , Lipid Peroxides/metabolism , Oxidation-Reduction , Tandem Mass Spectrometry/methodsABSTRACT
S-Glycosyl thiosulfates have been discovered as a new class of synthetic intermediates in sugar chemistry, named "glycosyl Bunte salts" after 19th-century German chemist, Hans Bunte. The synthesis was achieved by direct condensation of unprotected sugars and sodium thiosulfate using a formamidine-type dehydrating agent in water-acetonitrile mixed solvent. The application of glycosyl Bunte salts is demonstrated with transformation reactions into other glycosyl compounds such as a 1-thio sugar, a glycosyl disulfide, a 1,6-anhydro sugar, and an O-glycoside.
