Figure 1

The H₂N-HAIYPRH-CONH₂ peptide BBB shuttle (1 L): (a) light and (b) heavy versions containing an isotopically labeled acetyl moiety; and (c) the library of analogs of the parent (HAI or 1 L) on the left, and the retro-D-version (rD-HAI or 6D) and its analogous modifications on the right.