The scope of Viedma ripening and temperature cycling with respect to chiral molecules has remained mostly limited to molecules with a single stereogenic center, while racemization proceeds through inversion at that particular stereocenter. In this article we demonstrate for the first time that atropisomers, chiral rotamers that possess an axis of chirality, can be successfully deracemized in th...

The synthesis of a new series of cyclopentadienylruthenium catalysts with varying electronic properties and their application in racemization of secondary alcohols are described. These racemizations involve two key steps: 1) β-hydride elimination (dehydrogenation) and 2) re-addition of the hydride to the intermediate ketone. The results obtained confirm our previous theory that the electronic p...

A new, dynamic diastereomeric crystallization method has been developed, in which the mother liquors are continuously separated, racemized over a fixed-bed catalyst, and recirculated to crystallizer resolution–racemization–recycle (R3) process. Separating racemization from overcomes problems of using catalysts situ, that suffer conflicting sets conditions, inhibition, separation. Continuous ach...

The water accessibilities to aspartyl residues at positions 7 and 23 in the amyloid ß 1 -28 peptide associated with Alzheimer’s Disease have been calculated using different techniques. These accessibilities of water were compared to those of the succinimidyl residues (SUC) replacing the aspartyl ones (ASP). It has been possible to ascertain that these modifications (ASP —»• SUC) lead to a signi...

A low-energy pathway for pentathiepin racemization has been found using density functional theory (DFT) calculations. 3-[1,2,3,4,5]pentathiepin-6-yl-propylamine served as a model compound for tunicate-derived pentathiepins. Pentathiepin racemization becomes a low-energy process in the presence of a thiolate ion nucleophile. It is unknown whether the biosynthetic process for pentathiepins is ena...

The rapid racemization of aspartic acid (Asp) residues in peptides and proteins is due mainly to the succinimide intermediate. However, there should be another mechanism for Asp racemization without intermediacy of the succinimide. The direct H-atom abstraction from the C(alpha)-atom that leads to the enol form of the Asp residue is one possibility. In another study, we have computationally pre...

D-amino acids exist in living organisms as specialized components of many different machineries. Biosynthesis of D-amino acids from racemization of predominant L-enantiomers is catalyzed by a single enzyme. Here, we report the finding of a novel 2-component amino acid racemase for D-to-L inversion in D-arginine metabolism of Pseudomonas aeruginosa. From DNA microarray analysis, the putative dau...

Phosphonium and uronium salt-based reagents enable efficient and effective coupling reactions and are indispensable in peptide chemistry, especially in machine-assisted SPPS. However, after the activating and coupling steps with these reagents in the presence of tertiary amines, Fmoc derivatives of Cys are known to be considerably racemized during their incorporation. To avoid this side reactio...

α-Crystallin is one of the major proteins in the vertebrate eye lens and its function has been indicated to be maintenance of lens transparency. α-Crystallin exists in the lens fiber cell cytoplasm as a polydisperse aggregate with an average molecular mass of approximately 800 kDa. The aggregate is composed of two kinds of polypeptides, αAand αB-crystallins, containing 173 and 175 amino acid re...

If amino-acids are treated in glacial acetic acid solution with the theoretical amount of acetic anhydride, optically active acetamino-acids are obtained, while if a large excess of acetic anhydride is used, racemization and/or formation of azlactones takes place [Bergmann et al. 1926; Bergmann & Zervas, 1928]. Excess of acetic anhydride causes racemization even in aqueous solution in the prese...