TABLE 2.

Synthesized TCPs with triphosphate bridge modifications

^7mG_3′-X 5′↔ 5′ A_mpG 2′-O-methyladenosine Series 2-A			^7mG_m 5′↔ 5′ ^6mA_mpG 2′-O-methyl-N⁶-methyladenosine Series 2-B
TCP	3'-X	↔	TCP	↔
2-1A	O-Me	pp	2-1B	pp
1-2A	O-Me	ppp	1-2B	ppp
2-2A	O-Me	pppp	2-2B	pppp
2-3A	O-Me	S-ppp	2-3B	S-ppp
2-4A12	O-Me	p(S)pp (D1 + D2)	2-4B12	p(S)pp (D1 + D2)
2-5A1	O-Me	pp(S)p (D1)	2-5B1	pp(S)p (D1)
2-5A2	O-Me	pp(S)p (D2)	2-5B2	pp(S)p (D2)
2-6A12	O-Me	ppp(S) (D1 + D2)	2-6B1	ppp(S) (D1)
2-7A	O-Me	ppp-S
2-8A	O-Me	ppNHp
2-9A	O-Me	ppCH₂p
2-10A	O-Me	ppp-vinyl
2-11A	OH	ppp-vinyl

(↔) (5′)-(5′)-bridge structure between ^7mG_m (or ^7mG) and A_mpG (or ^6mA_mpG) dinucleotide fragments of TCP. (S-ppp or ppp-S) Triphosphate bridge containing α- or γ-phosphorothiolate linkage, respectively; [ppp(S), pp(S)p, or p(S)pp] triphosphate bridge containing α-, β-, or γ-phosphorothioate linkage, respectively; (ppNHp and ppCH₂p) triphosphate bridge containing α-β bridging phosphoramido or phosphonate linkages, respectively; (ppp-vinyl) triphosphate bridge with α-phosphonate connected 5′-vinyl ribose. (D1) Diastereomer 1; (D2) diastereomer 2.

Novel trinucleotide mRNA capping reagents: improved synthetic route and efficient cotranscriptional incorporation in mRNA