Enzymes are indispensable tools in modern organic synthesis.
Recent progress in cloning techniques, microbiology and protein purification supply an ever growing number and quantity of preparatively useful biocatalysts. Initially used to synthesize compounds found in nature, enzymes are now probed on non-natural substrates to an increasing degree. They work on highly functional and unprotected substrates under mild and environmentally friendly conditions. The following article will focus on the application of glycosyltransferases in the area of molecular glycobiology. Selected reactions with non-natural substrates will be discussed.