New di:nucleotide analogues - with phosphoro:di:thioate or phosphoro:thio:amidate linkages

Dinucleotide analogues of formula (I) are new, where A = H, OH, halogen, SH, NH2, N3, OR4, SR4 or -NR4 [sic], where R4 is an opt. heteroatom-substd. blocking gp.; B = a nucleoside or deoxynucleoside base; R1 and R3 = H or blocking gps.; R2 = SR5, NHR6 , NR6R7 or a sulphur or oxygen double-bonded (sic) to the P atom; R5 = opt. heteroatom-substd. alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, alkenyl, cycloalkenyl, aralkenyl, alkynyl, aralkynyl or cycloalkynyl; R6 and R7 = opt. heteroatom-substd. alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, alkenyl, cycloalkenyl, aralkenyl, alkynyl, aralkynyl or cycloalkynyl, or NR6R7 = (a) a heterocyclic gp. contg. up to 5 ring C atoms and 0-5 pendant C atoms or (b) a satd. or unsatd. N-contg. heterocyclic gp. contg. at least one additional heteroatom selected from N, O and S.