SPACER EFFECT ON THE SYNTHESIS OF OLIGODEOXYNUCLEOTIDES BY THE PHOSPHITE METHOD.

Nineteen oligonucleotides of 15-27 bases long were synthesized on aminoalkyl spacers of various chain lengths, Si-O-(CH//2)//3NHCONH(CH//2)//nNHCO(CH//2)//mNH//2, linked to Fractosil silica gel supports (F6, F12, F15, F18, F21, F24, F32, F38), to Porasil (P15) silica gel support, and to modified controlled pore glass (CPG17, CPG24). The purity and the homogenity of the end product in the reaction mixture was quantitatively determined from the autoradiograph pattern of bands on polyacrylamide sizing gel. The data indicated that the most pure products are obtained either on the shortest spacer, F6, or on the 24, 32, or 38 atom length spacers. Spacer lengths of 15, 18 and 21 atoms gave very poor results, with large amounts of impurities. The results are interpreted on the basis of conformational changes in the spacer alkyl chain as a function of its length.