Nonenzymatic Exogenous and Endogenous Antioxidants

Nonenzymatic exogenous and endogenous antioxidants play an important role in human health and act as preservatives for cosmetics, pharmaceuticals, and food products. This chapter will discuss the chemical structure and mechanism of action of the most important nonenzymatic small exogenous and endogenous organic molecules that act as antioxidants. The chapter will focus on the structural features, functional groups, properties, biosynthetic origin, and mechanism of action of such antioxidants. It also covers damages that free radicals create and the mechanisms by which they are neutralized by the various antioxidants. The scope of this chapter will be limited to nonenzymatic exogenous and endogenous antioxidants since enzymatic antioxidants have been discussed extensively in several reviews

The Unconserved Groucho Central Region Is Essential for Viability and Modulates Target Gene Specificity

Groucho (Gro) is a Drosophila corepressor required by numerous DNA-binding repressors, many of which are distributed in gradients and provide positional information during development. Gro contains well-conserved domains at its N- and C-termini, and a poorly conserved central region that includes the GP, CcN, and SP domains. All lethal point mutations in gro map to the conserved regions, leading to speculation that the unconserved central domains are dispensable. However, our sequence analysis suggests that the central domains are disordered leading us to suspect that the lack of lethal mutations in this region reflects a lack of order rather than an absence of essential functions. In support of this conclusion, genomic rescue experiments with Gro deletion variants demonstrate that the GP and CcN domains are required for viability. Misexpression assays using these same deletion variants show that the SP domain prevents unrestrained and promiscuous repression by Gro, while the GP and CcN domains are indispensable for repression. Deletion of the GP domain leads to loss of nuclear import, while deletion of the CcN domain leads to complete loss of repression. Changes in Gro activity levels reset the threshold concentrations at which graded repressors silence target gene expression. We conclude that co-regulators such as Gro are not simply permissive components of the repression machinery, but cooperate with graded DNA-binding factors in setting borders of gene expression. We suspect that disorder in the Gro central domains may provide the flexibility that allows this region to mediate multiple interactions required for repression

Catalytic enantioselective conjugate addition of grignard reagents to cyclic enones using C 1 -1,1′-bisisoquinoline-based chiral ligands

New highly constrained chiral C1-1,10-bisisoquinoline ligands were examined in the enantioselective conjugate addition of Grignard reagents to cyclohexenone and cyclopentenone. The desired 1,4-adducts were obtained in excellent yield and moderate enantiomeric excess (up to 35%)

Efficient, one-step, cascade synthesis of densely functionalized furans from unprotected carbohydrates in basic aqueous media

Condensation of unprotected carbohydrates with malononitrile or malonamide nitrile in basic aqueous media gave in one-pot densely functionalized polyhydroxyalkyl 2-amino-3-furanonitriles and polyhydroxyalkyl 2-amino-3-furanocarboxamides in excellent 84–98% yields. Disaccharides afforded novel furano-glycosides. Based on the rate of formation of the furans, the ability of the tested bases to catalyze the reaction was concluded as Et₃N > DBU > K₂CO₃ > NaOMe. The reaction mechanism involved the formation of bicyclic furan-furan and furan-pyran intermediates observed for the first time. The reaction proceeded through a cascade mechanism involving Knoevenagel condensation, Oxo-Micheal addition, Thorpe-Ziegler type reaction and ring-opening-induced aromatization. This operationally simple and metal-free reaction proceeded with exclusive chemo-, regio-, and stereo-selectivities under environmentally benign conditions. As demonstrated on a 2 g scale, it holds promise for application in the large-scale synthesis of important intermediates such as densely functionalized furfural.Nanyang Technological UniversityWe thank Nanyang Technological University, Singapore for financial help (RG 142/16)

Short synthesis of phenylpropanoid glycosides calceolarioside A and syringalide B

An efficient and practical three-step synthesis of phenylpropanoid glycosides calceolarioside A and syringalide B in >62% overall yield is disclosed. The key step involves the chemoselective and regio selective direct O-4 cinnamoylation of unprotected 2-phenylethyl-β-d-glucosides with cinnamic anhydrides using a chiral 4-pyrrolidinopyridine organocatalyst. This approach serves as a model for the short synthesis of phenylpropanoid glycosides acylated at O-4 without protection/deprotection steps

Selective one-pot multicomponent synthesis of N-substituted 2,3,5-functionalized 3-cyanopyrroles via the reaction between α-hydroxyketones, oxoacetonitriles, and primary amines

A one-step, three-component reaction between α-hydroxyketones, oxoacetonitriles, and primary amines gives N-substituted 2,3,5-functionalized 3-cyanopyrroles with complete selectivity in up to 90% isolated yields. The reaction worked on a wide substrate scope under mild reaction conditions (AcOH as a catalyst, EtOH, 70 °C, 3 h). The reaction proceeded with very high atom efficiency as water is the only molecule lost during the reaction. The practicality of the reaction was demonstrated on a large gram scale. The structures of the 3-cyanopyrroles were confirmed by single-crystal X-ray diffraction and NMR; this work provides a general and practical entry to pyrrole scaffolds suitably decorated for the synthesis of various bioactive pyrroles in a concise manner.Nanyang Technological UniversityPublished versionThis research was funded by the College of Engineering (Startup Grant), Nanyang Technological University, Singapore and by United Arab Emirates University (UAEU), Al-Ain (Grant no. G00003291/Fund no. 31S401/12S040/Project #852)