of formula Ara???H, wherein Ara is as defined above; or (c) reacting a compound of formula (III) wherein R1a, q and R2a are as defined above and M??? represents a metal residue (eg. sodium); with a compound of formula Ara-L2, wherein Ara is as defined above and L2 represents a suitable leaving group (eg. a halogen atom such as chlorine or bromine) and thereafter, as necessary, deprotecting a prot