A broad variety of new acyclic vinyl ethers (see 6-41) have been synthesized viu the vinyl-interchange reaction of ethyl vinyl ether at room temperature using mercury(I1) trifluoroacetate as a highly efficient catalyst. The appropriate vinyl ethers were reacted under acidic conditions with 3',5'-0-silyl-protected uridine 42 to the corresponding 2-0-(1-alkoxyethyl) derivatives 43 --83 which gave, on desilylation of Fions, in high yields the uridinc-2-0-acetal derivatives 84-124. The relative stabilities of the newly synthesized compounds under acidic and basic conditions were determined using TLC and HPLC techniques. Protected protecting groups offer the best properties for oligoribonucleotide syntheses. Interestingly, the very acid-stable acetals of the /$substituted ethyltype 118-121 and 123 can be cleaved by a [Mimination process providing a series of base-labile acetals of potcntial synthetic value. HFLVETICA CHIMICA ACTA -VOI 81 (1998) Scheme 2 -, P H Me H Me 43 -83 84 -124 42 6 -4 1 C1 H SO
New blocking group combinations for the machine-aided oligoribonucleotide synthesis on solid phase material have been developed and tested regarding their general application. An acetal function for 2'-OH protection offers a series of advantages in the synthetic approach but special conditions have to be fulfilled in order to guarantee a selective cleavage of the temporary 5'-OH blocking group such as the dansylethoxycarbonyl or even the acid-labile dimethoxytrityl group in the chain elongation process. The final removal of the 2'-O-acetal function in the partially deblocked oligomer proceeds unexpectedly well under weak acidic conditions due to a supposed intramolecular acid catalysis.
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