The search for new and effective chiral selectors capable of separating a wide variety of enantiomeric compounds is an ongoing process. In the past decade, macrocyclic antibiotics have proved to be an exceptionally useful class of chiral selectors for the separation of enantiomers of biological and pharmacological importance by means of HPLC, TLC and electrophoresis. More chiral analytes have been resolved through the use of glycopeptides than with all the other macrocyclic antibiotics combined (ansamycins, thiostrepton, aminoglycosides, etc.). The glycopeptides avoparcin, teicoplanin, ristocetin A and vancomycin have been extensively used as chiral selectors in the form of chiral bonded phases in HPLC, and HPLC stationary phases based on these glycopeptides have been commercialized. Teicoplanin, vancomycin, their analogs and ristocetin A seem to be the most useful glycopeptide HPLC bonded phases for the enantioseparation of proteins and unusal native and derivatized amino acids. In fact, the macrocyclic glycopeptides are to some extent complementary to one another: where partial enantioresolution is obtained with one glycopeptide, there is a high probability that baseline or better separation can be obtained with another. This review sets out to characterize the physicochemical properties of these antibiotics and their application in the enantioseparations of amino acids. The mechanism of separation, the sequence of elution of the stereoisomers and the relation to the absolute configuration are also discussed.

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Apolipoprotein E4 (apoE4) is the most prevalent genetic risk factor for Alzheimer's disease (AD). Epidemiological studies revealed that consumption of docosahexaenoic acid (DHA: 22 : 6 (ω3)), a major brain polyunsaturated fatty acid, is protective for AD and that elevated cholesterol levels are an AD risk factor. We presently investigated the extent to which the pathological effects of apoE4 in vivo can be prevented by consuming fish oil (DHA) or can be modified by cholesterol. Accordingly, apoE3- and apoE4-targeted replacement mice were subjected, following weaning, to a fish oil diet enriched in DHA and to a cholesterol-containing diet under regular and enriched environments. Cholesterol metabolism in the hippocampus and the corresponding phospholipid and fatty acid levels were affected by fish oil (DHA) and cholesterol diets and by environmental stimulation. Importantly, cholesterol metabolism and the fatty acid levels were not affected by apoE4. The phospholipid levels were, however, affected by apoE4. This effect was most pronounced in the cholesterol-fed mice and was abolished by the fish oil (DHA) diet. ApoE4 elevated hippocampal intraneuronal amyloid-β levels under regular conditions and lowered them following environmental stimulation, relative to those of the apoE3 mice. ApoE4 also elevated the levels of the presynaptic transporters Vglut and Vgat, and decreased behavioral performance in an object recognition test. Importantly, all of these apoE4 phenotypes were abolished by the fish oil (DHA) diet, whereas the cholesterol diet modified them. These findings suggest that a fish oil (DHA) diet could be used to attenuate the effects of apoE4 in AD.