Benzyl (Bzl) an alkyl residue and a side-chain protecting group employed in Boc/Bzl-based SPPS and solution synthesis. Bzl is commonly used for blocking alcohols (Ser, Thr, Hyp), it is cleaved by strong acids or catalytic hydrogenolysis (e.g. hydrogen/Pd). Deblocking of N-Bzl and S-Bzl requires much harsher conditions. The acid lability of benzyl ethers, esters (see OBzl), thiols, and amines can be modulated by introducing  substituents at the α-carbon or the aromat, e.g. halogens for improving or α-substituents for decreasing the acid stability.