R is OR¹, or NR²R³, wherein R is at the ortho, meta, meta', or para position relative to the NH substituent of Formula I;

X is O, C═O, NR⁴, S, S═O, or S(═O)₂;

G^x is a moiety of Formula X1 or X2;

Y is H, OH, halo, or Me;

Z is OH, O(dimethoxytrityl), guanidinium, phosphate, diphosphate, triphosphate, phosphoramidite, phosphorothioate, or —O₂P(═O)(3′ -X1A) wherein Formula X1A is,

R^z is H, —P(N(R⁴)₂)(OCH₂CH₂CN), or —O₂P(═O)(5′-X1A);

R¹ is CH₂CH₃ or (C₃-C₁₂)alkyl wherein alkyl is optionally branched;

R² and R³ are each independently CH₃, CH₂CH₃, or (C₃-C₁₂)alkyl wherein alkyl is optionally branched;

R⁴ is H, CH₃, or CH₂CH₃, CH(CH₃)₂;

each Q is independently H, CH₃, CH₂CH₃, (C₃-C₁₂)alkyl wherein alkyl is optionally branched, or —(CH₂CH₂O)n(C₁-C₄)alkyl where n is 1-20, and when Q is not H the carbon of the CH—Q bond is a stereocenter having an (R)-configuration, or an (5)-configuration;

R^A is H, CH₃, CH₂CH₃, (C₃-C₁₂)alkyl wherein alkyl is optionally branched, or an amide bond to X2A wherein Formula X2A is:

R^B is H, CH₃, CH₂CH₃, (C₃-C₁₂)alkyl wherein alkyl is optionally branched, or a protecting group;

R^C is OH, OCH₃, OCH₂CH₃, O(C₃-C₁₂)alkyl wherein alkyl is optionally branched, or an amide bond to X2A;

each J is independently O or S, and when J is S the phosphorous stereocenter has an (R)-configuration, or an (S)-configuration;

each W is independently adenine (A), thymine (T), cytosine (C), guanine (G), or Formula IA, wherein Formula IA is,

d is 1 to about 50.