1,2,3,4-Tetrahydro-5-(2-oxiranylmethoxy)-(2R,3S)-rel-2,3-naphthalenediol-D5 is an isotopic labelled analog of 1,2,3,4-tetrahydro-5-(2-oxiranylmethoxy)-(2R,3S)-rel-2,3-naphthalenediol. 1,2,3,4-Tetrahydro-5-(2-oxiranylmethoxy)-(2R,3S)-rel-2,3-naphthalenediol is used as a reactant in the synthetic preparation of Nadolol (cis-5-{3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy}-1,2,3,4-tetrahydro-2,3-naphthalenediol) which is a β-adrenergic blocking agent.