Mini-Reviews in Organic Chemistry - Volume 6, Issue 3, 2009

The asymmetric hydrosilylation of ketones and imines has seen significant advances in the last decade. The discovery of new highly efficient catalysts has turned this catalytic process into an attractive method for practical applications. Impressive chemical yields and enantioselectivities have been attained employing newly designed catalytic systems based on rhodium, copper, zinc and iron with suitable bidentate chiral ligands.

Aminolysis of organic carbonates is a suitable phosgene-free synthetic route to carbamate esters. The paper reviews recent advances in this field. Emphasis is laid on the reaction of amines with industrially relevant carbonic acid diesters, (MeO)2CO, (PhO)2CO, MeOC(O)OPh, currently obtainable without using phosgene. The carbonylation process may require a catalyst. The use of effective catalytic systems is highlighted and their mode of action is discussed.

This review summarizes the interesting results obtained during the last decade in the radical aminoalkylation of a wide range of nucleophilic radicals (deriving from hydrocarbons, ethers, alcohols, halogenated derivatives and amides) promoted by transition metals. We focus on the two main procedures which recently yielded the most relevant results in this field: the dimethylzinc-air process and the new Porta reaction, based on the Ti(III)/hydroperoxide system. These protocols often provide competitive alternatives to classical landmark transformations, like the Mannich reaction and the Strecker synthesis. Moreover, a brief overview of other significant examples is given in the last section of the review.

One of the most challenging areas in the field of peptide science is the chemistry of cysteine and the need for multiple protecting groups that can be removed orthogonally to facilitate regioselective disulfide bond formation. This article reviews the methods and reagents used to remove the various protecting groups of cysteine derivatives with subsequent disulfide bond formation used in peptide synthesis. Also reviewed is the related amino acid selenocysteine, which requires benzyl-type protecting groups during synthesis. As these benzyl groups are difficult to remove using older methods, we highlight the use of electrophilic, aromatic disulfides for the removal of selenocysteine (and cysteine) protecting groups with concomitant disulfide and diselenide bond formation.

Lutein ((all-E,3R,3'R,6'R)-β,η-carotene-3,3'-diol) is the main carotenoid that can be found in light-harvesting complexes of higher plants and it is also involved in human diet. In the extracts of human plasma the 3'-epimer of lutein, several geometrical isomers, dehydration and oxidation products of lutein have been identified. It was also established that lutein reduces the risk of AMD (age-related macular degeneration). This mini review focuses on the in vitro and in vivo transformations of lutein.

Being the pyrazolo[3,4-d]pyrimidine ring system isoster with the adenine scaffold of ATP, many synthetic approaches for the construction of this bicyclic system have been developed in the last fifty years in order to identify novel bioactive molecules. The synthesis of 4-amino-pyrazolo[3,4-d]pyrimidine derivatives together with the functionalization of the core structure have been reviewed. The evolution of the scaffold from the pioneering work of Robins to the recent preparation of selective pharmacologically active molecules is discussed in terms of synthetic methodologies to produce biologically active compounds. With the literature on pyrazolo[3,4- d]pyrimidines particularly beings rich, the focus of this review deals with the construction of the ring system from pyrazoles only, reporting same selected examples in this branch of chemistry.

Microgels obtained by miniemulsion polymerization are highly cross-linked but soluble polymer particles with sizes between 10 and 600 nm. This property renders them useful not only as platforms for molecular recognition and sensing of biomolecules, but also as colloids that participate in catalysis. Recent approaches employing catalytically active templated and non-templated microgels are highlighted