The present invention relates to novel synthesis routes for preparation of thiodigalactosides of the general formula (12) The method comprises the use of a 3-azido-galactosyl thiouronium salt derivative, which is activated to the corresponding thiol in situ, which in turn is directly reacted with a 3-azido-galactosyl bromide resulting in the 3,3-di-azido-thio-di-galactoside before the thiol has a chance to reduce the azido group. Hence, in situ formation of the 3-azido-galactosyl thiol from the thiouronium salt is essential in the synthesis procedure, because any other method that generate the thiol separately results in extensive unwanted azide reduction.
