The invention provides ribonucleoside derivatives with novel protecting groups and methods for the preparation of such ribonucleoside derivatives. The general formula (I) of the ribonucleoside derivatives is: wherein R.sub.1 is a base of the purine- or pyrimidine-family or a derivative of such a base or any other residue with serves as a nucleobase surrogate, R.sub.2 is a proton or a substituted derivative of phosphonic acid, R.sub.3 is a proton or a protection-group for the oxygen atom in 5'-position, R.sub.4, R.sub.5 and R.sub.6 are independently alkyl or aryl or a combination of alkyl and aryl or heteroatom, R.sub.4, R.sub.5 or R.sub.6 may also be cyclically connected to each other; and wherein at least one of the R.sub.4, R.sub.5 or R.sub.6 substituents comprises a tertiary C-atom or a heteroatom vicinal to the Si-atom.