Cell surface proteolysis is essential for communication between cells and results in the shedding of membraneprotein ectodomains. However, physiological substrates of the contributing proteases are largely unknown. We developed the secretome protein enrichment with click sugars (SPECS) method, which allows proteome-wide identification of shedding substrates and secreted proteins from primary cells, even in the presence of serum proteins. SPECS combines metabolic glycan labelling and click chemistry-mediated biotinylation and distinguishes between cellular and serum proteins. SPECS identified 34, mostly novel substrates of the Alzheimer protease BACE1 in primary neurons, making BACE1 a major sheddase in the nervous system. Selected BACE1 substrates-seizureprotein 6, L1, CHL1 and contactin-2-were validated in brains of BACE1 inhibitor-treated and BACE1 knock-out mice. For some substrates, BACE1 was the major sheddase, whereas for other substrates additional proteases contributed to total substrate shedding. The new substrates point to a central function of BACE1 in neurite outgrowth and synapse formation. SPECS is also suitable for quantitative secretome analyses of primary cells and may be used for the discovery of biomarkers secreted from tumour or stem cells.

Fully protected tetra-, hexa-and octasaccharides of hyaluronic acid were synthesized on a scale of several 100 mg up to gram quantities usingpyranoside as a key building block. This disaccharide was subjected to deprotection, then glycosylation via the trichloroacetimidate method was employed to achieve the formation of the oligosaccharides.

SummarySugar moieties are present in a wide range of bioactive molecules. Thus, having versatile and fast methods for the decoration of biomimetic molecules with sugars is of fundamental importance. The glycosylation of peptoids and polyamines as examples of such biomimetic molecules is reported here. The method uses Cu-catalyzed azide alkyne cycloaddition to promote the reaction of azidosugars with either polyamines or peptoids. In addition, functionalized nucleic acids were attached to polyamines via the same route. Based on a modular solid-phase synthesis of peralkynylated peptoids with up to six alkyne groups, the latter were modified with azidosugar building blocks by using copper-catalyzed azide alkyne cycloadditions. In addition, the up-scaling of some particular azide-modified sugars is described.

A series of diastereomeric fluorinated and nonfluorinated triazolo analogues of naturally occurring sphingolipids like dihydroceramide suitable for physicochemical and medicinal chemistry applications were prepared enantioselectively. Key steps of the synthetic sequence are asymmetric Sharpless dihydroxylation of a,bunsaturated esters to diols, regioselective ring opening of derived cyclic sulfates by azide, 1,3-dipolar cycloaddition with alkynes, and reduction of the ester groups.

The synthesis of a series of different fluorinated analogues of sphinganine and dihydroceramide using Staudinger ligation of diastereomeric 2-azido-4-fluoro-3-hydroxyoctadecanoates and subsequent selective ester reduction as key steps is presented. The formed sphingolipid analogues are interesting for medicinal studies as well as for the investigation of their phase behavior at interfaces.