Conversions structural diversity

Abstract An overview on the microwave-enhanced synthesis and decoration of the 2(lH)-pyrazinone system is presented. Scaffold decoration using microwave-enhanced transition-metal-catalyzed reactions for generating structural diversity, as well as the conversion of the 2(lH)-pyrazinone skeleton applying Diels-Alder reactions to generate novel heterocyclic moieties are discussed. The transfer of the solution phase to polymer-supported chemistry (SPOS) is also described in detail. 

An important procedure for the synthesis of cyclopentenones is the so-called Pauson-Khand reaction, which constitutes a formal [2 + 2 + 1] cycloaddition of an alkene, an alkyne, and carbon monoxide. Due to the increase in structural diversity of the available starting materials, the reaction has become an attractive target for scientific investigations [1-8]. The first successful example was reported by Pauson, Khand et al [9] in 1973 for the conversion of norbornene with the phenylacetylene-hexacarbonyldicobalt complex to give the corresponding cyclopentenone in 45% yield (Eq. 1). 

II. Product Summaries BCI specializes in software for analysis of the structural diversity of large chemical dataset and combinatorial chemistry libraries. BCI s software covers Chemical Structure Fragments and Fingerprinting, Diversity Analysis, Cluster Analysis, and Structure or Reaction query format conversion (MOLSMART). 

Although the enzymes taking part in glycolysis and the subsequent conversion of pyruvate are structurally diverse,... 

The general reactivity of the A, B, and C rings of anthocyanins and other flavonoids results in a large number of potential products that may undei o further reactions. Given the large structural diversity of grape tannins (7) (5) (P)), a quasi-infinite number of reaction products, colored or not, may be formed in wines. Therefore, the conversion pathways of native components and their impact on wine sensory properties is difficult to define. 

In a similar fashion, resin-bound imines 109 were employed to prepare a library of structurally diverse P-lactams by [2+2] cycloaddition reactions with different ketenes. Thus, as shown in Scheme 4.1.22, amino acids tethered to the acid labile Sasrin resin (103) were condensed quantitatively to imines 109 by using a large excess of alkyl, aryl, or a,P-unsaturated aldehydes in a mixture of trimethylorthoformate and dichloromethane. Optimisation studies of the [2+2] cycloaddition step, showed that conversion to P-lactams 110 could only take place by slow addition of acid chlorides to a suspension of the imine resin at 0°C in the presence of triethylamine. By using a large excess of ketene at high concentration, the cycloaddition of imines derived from even sterically hindered amino acids [e.g. valine) could be carried out with full conversion. After mild TFA cleavage from the resin and preparative HPLC purification, the p-lactams 111, 112 were isolated in yields of 55-97%. 

The structural diversity and labile nature of the bonds that link the various building blocks have posed a serious challenge to the characterization of glycol-ipids. Complete structural characterization of GSLs requires structure elucidation of the constituents of the ceramide and sugar portions. In a classical mass spectrometry method, glycolipids are cleaved into individual structural units and are analyzed by EI-MS or GC/MS after conversion to a suitable derivative, such as by the acetylation, permethylation, or permethylation-reduction reaction. 

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