O-(4-Methoxybenzyl)hydroxylamine hydrochloride is a specialized reagent in organic synthesis, primarily employed for the selective formation of O-(4-methoxybenzyl)oximes from aldehydes and ketones. These oximes act as protected forms of carbonyl groups, facilitating controlled manipulation in multi-step reactions for the synthesis of complex molecules, including pharmaceuticals, natural products, amino sugars, and glycosidase inhibitors. The 4-methoxybenzyl (PMB) group provides stability and can be orthogonally removed under mild acidic conditions, enhancing its utility in sensitive synthetic sequences. Additionally, it supports efficient coupling reactions in peptide and nucleoside chemistry, and is widely used in research for preparing intermediates in drug discovery.