Three liquid-phase processes for the elaboration of short orthogonally prot
ected PNA have been devised. Two of these methods are similar to the conver
gent and divergent approaches in peptide synthesis. The third process consi
sts in building a fully protected polyamide backbone, by using as many diff
erent and orthogonal protecting groups as there are different types of nucl
eic bases in the targeted polyPNA. Simultaneous and selective cleavage of o
ne kind of protecting group allows the simultaneous attachment of several i
dentical nucleobase units. (C) 1999 Elsevier Science Ltd. All rights reserv
ed.