SYNTHESIS AND PROPERTIES OF OLIGODEOXYRIBONUCLEOTIDE POLYETHYLENE-GLYCOL CONJUGATES

Pools of oligonucleotide conjugates consisting of 10 - 400 different m olecular species were synthesized. The conjugates contained a varying number of ethylene glycol units attached to 3'-terminal, 5'-terminal a nd internal positions of the oligonucleotides. Conjugate synthesis was performed by phosphoramidite solid phase chemistry using suitably pro tected polyethylene glycol phosphoramidites and PEG-derivatized solid supports containing polydisperse PEGs of various molecular weight rang es. The pools were analyzed and fractionated by chromatographic and el ectrophoretic techniques, and the composition of isolated conjugates w as revealed by matrix-assisted laser desorption/ ionization mass spect rometry. The number and attachment sites of coupled ethylene glycol un its greatly influence the hydrophobicity of the conjugates, as well as their electrophoretic mobilities. Conjugation had little effect on th e hybridization behavior of oligonucleotide conjugates with unmodified complementary oligonucleotide strands. Melting temperatures were betw een 67 and 73 degrees C, depending on the size and number of coupled P EG chains, compared to 68 degrees C for the unmodified duplex. Conjuga tes with PEG coupled to both 3'- and 5'-terminal positions showed a mo re than 10-fold increase in exonuclease stability.