(2S,4S)-5-(Biphenyl-4-yl)-4-[(tert-butoxycarbonyl)amino]-2-methylpentanoic acid is a chiral, non-proteinogenic amino acid derivative. It features a biphenyl group, a tert-butoxycarbonyl (Boc) protected amino group, and a carboxylic acid terminus, making it a versatile building block in medicinal chemistry. This compound is a key advanced intermediate in the synthesis of Aliskiren (Tekturna/Rasilez), a direct renin inhibitor used for the treatment of hypertension (high blood pressure). The (2S,4S) stereochemistry is crucial for the biological activity of the final drug molecule. Its structure allows for further coupling and deprotection steps to construct the complete Aliskiren framework. As a Boc-protected amino acid with a lipophilic biphenyl side chain, it is specifically designed for pharmaceutical synthesis rather than as a general-purpose reagent. Its primary value lies in enabling efficient, stereocontrolled production of this important cardiovascular API.