The present teachings provide methods, compositions, and kits for synthesizing and sequencing nucleic acids. In some embodiments, reversible di-nucleotide compounds are employed along with cleaving reactions that remove a label and a blocking moiety. Improved sequencing efficiency is achieved by the rapid polymerase-mediated incorporation of reversible di-nucleotide compounds. In some embodiments, the di-nucleotides do not contain conventional nucleotide triphosphates, but rather employ amino acid phosphoramidate nucleotides (AAPNs).