The synthesis of special CPG supports for the preparation of required oligonucleotide probes are shown in Schemes 1-3. Methyl 3-(3-chloro-2,4-dihydroxyphenyl) propanoate (4a) (Scheme 1) was synthesized starting from 3-chloro-2,4dimethoxybenzaldehyde (1) (20) , which was converted to substituted cinnamic acid 2 by Knoevenagel condensation. Intermediate 2 was hydrogenated in the presence of Pd/C to yield substituted phenyl propionic acid 3, which was first demethylated with HBr/HOAc and then converted to the methyl ester 4a.