Aminoacyl derivatives of nucleosides, nucleotides, and polynucleotides. V. Preparation of 2'(3')-O-(L-valylglycyl)-, 2'(3')-O-(L-lysylglycyl)-, and 2'(3')-O-(N-acetylglycyl)adenosine with the use of 2',3'-O-aminomethylethoxymethyleneadenosine as the key intermediate