TABLE 1.

Synthesized TCPs with ^7mG substituted at 2′- and/or 3′-ribose position^a

^7mG_{2′-R 3′-K} ppp A_mpG 2′-O-methyladenosine Series 1-A			^7mG_{2′-R 3′-K} ppp ^6mA_mpG 2′-O-methyl-N⁶-methyladenosine Series 1-B
TCP	2′-R	3′-K	TCP	2′-R	3′-K
1-1A	OH	OH	1-1B	OH	OH
1-2A	OH	O-methyl	1-2B	OH	O-methyl
1-3A	O-methyl	OH	1-3B	O-methyl	OH
1-4A	O-methyl	O-methyl	1-4B	O-methyl	O-methyl
1-5A	OH	S-methyl	1-5B	OH	S-methyl
			1-6B	OH	O-azidomethyl
1-7A	O-propargyl	OH	1-7B	O-propargyl	OH
1-8A	OH	NH-C(O)-CH₃	1-8B	OH	NH-C(O)-CH₃
1-9A	OH	O-methoxyethyl	1-9B	OH	O-methoxyethyl
1-10A	OH	F	1-10B	OH	F
1-11A	2′-4′-LNA	OH	1-11B	2′-4′-LNA	OH
1-12A	OH (Me)	OH	1-12B	OH (Me)	OH
1-13A	OH (l-ribose)	OH (l-ribose)	1-13B	OH (l-ribose)	OH (l-ribose)
			1-14B	Acyclo
			1-15B	2′,3′-O-isopropylidene
			1-16B	2′,3′-cyclic phosphate

(2′-4′-LNA) A d-ribose with 2′-4′ methylene bridge (locked nucleic acid); [OH(Me)] 2′-C-methyl-β-d-ribofuranosyl, [OH(l-ribose)] ^7mG with l-ribose sugar.
^aDetailed chemical structures are shown in Supplemental Table S2.

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