New trityl linkers for use in solid phase synthesis comprise compounds of formula II ##STR1## wherein R.sub.4 is alkyl (e.g. C.sub.1-4 alkyl), halogen, NO.sub.2, or hydrogen; Z is a coupling group chosen from acylamido, acyloxy, amino, halogen, thiol or hydroxyl, where acyl is the residue of a carboxylic acid or a residue of formula R.sub.5 CO where R.sub.5 is an organic group; Y is H, a reactive functional group or an attachment to a solid phase; W is O when Y is H or a reactive functional grou...