Imidazole, oxazole and thiazole alkaloids

Electrochemically promoted synthesis of polysubstituted oxazoles from β-diketone derivatives and benzylamines under mild conditions

An efficient electrochemical route has been developed to synthesize polysubstituted oxazoles, without the use of hazardous oxidants and transition metal catalysts.

Synthesis and biological evaluation of 1,7,8,8a-tetrahydro-3H-oxazolo[3,4-a]pyrazin-6(5H)-ones as antitumoral agents

A series of 1,7,8,8a-tetrahydro-3H-oxazolo[3,4-a]pyrazin-6(5H)-ones has been synthesized by an intramolecular, palladium(II) catalyzed, aminooxygenation of alkenyl ureas, readily available from glycine allylamides as starting materials. Biological tests showed that the obtained compounds are endowed with an interesting antitumoral activity against two human thyroid cancer cell lines, namely FTC-133 and 8305C, by promoting the apoptotic pathway and DNA fragmentation.

A simple route for the synthesis of novel N-alkyl-2-(alkylthio)-1H-imidazole derivatives

Novel N-alkyl-2-(alkylthio)-1H-imidazole derivatives were synthesized in a single step by an efficient and simple method in high yields. Readily available starting materials, mild reaction conditions, operational simplicity and novelty are the key advantages of this method. Besides their novel structures, these compounds may have important biological activities and industrial applications.

Hantzsch based macrocyclization approach for the synthesis of thiazole containing cyclopeptides

An innovative macrocyclization approach via high-yielding solid-phase intramolecular thioalkylation reaction is described. The reaction of S-nucleophiles with newly generated N-terminal 4-chloromethyl thiazoles leads to the desired cyclic products in high purities and good yields.

Hydrogen-bond-mediated asymmetric cascade reaction of stable sulfur ylides with nitroolefins: scope, application and mechanism

A hydrogen-bond-mediated asymmetric [4+1] annulation/rearrangement cascade of stable sulfur ylides and nitroolefins was developed. This reaction provides a facile route to enantioenriched 4,5-substituted oxazolidinones in moderate to excellent isolated yields (65-96 %) with excellent stereocontrol (up to more than 95:5 d.r. and 97:3 e.r.). This methodology was successfully applied to the concise synthesis of two bioactive molecules. The stereocontrolled modes and mechanism have been proposed to explain the origin of this stereochemistry.

Communication: Where does the first water molecule go in imidazole?

Supersonic jet FTIR spectroscopy supplemented by (18)O substitution shows unambiguously that water prefers to act as an O-H···N hydrogen bond donor towards imidazole, instead of acting as a N-H···O acceptor. Previous matrix isolation, helium droplet, and aromatic substitution experiments had remained ambiguous, as are standard quantum chemical calculations. The finding is supported by a study of the analogous methanol complexes and by higher level quantum chemical calculations.

Imidazole derivatives: a comprehensive survey of their recognition properties

Due to its amphoteric nature the imidazole ring can function as selective and effective anion and/or cation and even neutral organic molecules receptor system. As a result, the design of new multichannel imidazole-based receptors capable of recognizing different types of analytes is strongly demanded. This review summarizes the most recent and relevant advances in this area.

Catalyst-free preparation of 1,2,4,5-tetrasubstituted imidazoles from a novel unexpected domino reaction of 2-azido acrylates and nitrones

A highly efficient and convenient method for the synthesis of 1,2,4,5-tetrasubstituted imidazoles from readily accessible 2-azido acrylates and nitrones has been developed. This reaction proceeded under mild conditions without the assistance of any metal, acid, or base.

Biosynthesis, asymmetric synthesis, and pharmacology, including cellular targets, of the pyrrole-2-aminoimidazole marine alkaloids

The pyrrole-2-aminoimidazole (P-2-AI) alkaloids are a growing family of marine alkaloids, now numbering well over 150 members, with high topographical and biological information content. Their intriguing structural complexity, rich and compact stereochemical content, high N to C ratio (~1 : 2), and increasingly studied biological activities are attracting a growing number of researchers from numerous disciplines world-wide. This review surveys advances in this area with a focus on the structural diversity, biosynthetic hypotheses with increasing, but still rare, verifying experimental studies, asymmetric syntheses, and biological studies, including cellular target receptor isolation studies, of this stimulating and exciting alkaloid family.

Synthesis of spirocyclic thiazolidinediones using ring-closing metathesis and one-pot sequential ring-closing/cross metathesis

A novel synthetic route to spirocyclic thiazolidinediones is reported by utilizing ring-closing metathesis (RCM). A selective cross metathesis (CM) of N-allyl azaspiro derivatives with different olefins has been demonstrated to prepare substituted azaspiro-[4.4]nonenediones. The X-ray crystal structure of a spirocyclic thiazolidinedione dimer is described, which has been prepared in two steps from thiazolidinedione using a one-pot sequential ring-closing and self metathesis. Cross metathesis proceeds smoothly with both electron rich and poor olefins. The symmetrical bis-thiazolidinedione spirocyclic system can be used as CM coupling partner with olefins. One-pot sequential RCM-CM has been developed for the synthesis of substituted spirocyclic compounds. The methodology allows a quick access to thia-azaspiro-[4.4]nonene and -[4.5]decene-dione ring systems from readily available starting materials which are not otherwise accessible.

High Throughput Synthesis of 2,3,6-Trisubstituted-5,6-Dihydroimidazo[2,1-b]thiazole Derivatives

A facile approach to the synthesis of 2,3,6-trisubstituted-5,6-dihydroimidazo[2,1-b]thiazole was reported. A resin bound cyclic thiourea was formed by the treatment of a resin bound diamine with 1,1'-thiocarbonyldiimidazole, and then reacted with a α-haloketone to generate a resin bound isothiourea. HF treatment of the resin bound isothiourea resulted in the cleavage of the product and simultaneous formation of an enamine bond. This led to the formation of the 2,3,6-trisubstituted-5,6-dihydroimidazo[2,1-b]thiazole in high yield and purity.

2,3-Dichloro-5,6-dicyano-1,4-benzoquinone-catalyzed reactions employing MnO2 as a stoichiometric oxidant

Several oxidative reactions can be effected with MnO(2) in the presence of substoichiometric quantities of DDQ. These transformations include oxidative cyclization, deprotection, and dehydrogenation reactions. The use of MnO(2) as a terminal oxidant for DDQ-mediated reactions is attractive based on economical and environmental factors.

A direct synthesis of oxazoles from aldehydes

An expedient method for the direct conversion of aldehydes to 2,4-disubstituted oxazoles is presented. The method relies on the oxidation of an oxazolidine formed from the condensation of serine with an aldehyde and proceeds through a 2,5-dihydrooxazole intermediate. In contrast to standard methods that start from carboxylic acids, the use of aldehydes as starting materials does not require intermediate purification and affords the oxazoles under relatively mild conditions.