• Formation of adamantyl esters has been used to block the ?-carboxyl group of aspartic acid in peptide synthesis. The 2-adamantyl ester is prepared using DCC-DMAP, is stable to TFA but can be cleaved with methanesulfonic acid: J. Chem. Soc., Perkin 1, 2129 (1988). See also Appendix 6.