Norethisterone enanthate (NET-EN) is a fatty acid ester of norethisterone. The single crystallographic data of NET-EN [a = 6.09236(14) Å, b = 12.7347(3) Å, c = 30.1234(8) Å, α = β = γ = 90°, unit-cell volume V = 2337.11 Å3, Z = 4, and space group P212121] were obtained by using acetone as a solvent. The interaction of NET-EN with human serum albumin (HSA) was investigated using different optical techniques and molecular modeling. The fluorescence quenching between NET-EN and HSA was a static quenching process. The fluorescence lifetime measurement provided us with an insight into the occurrence of static quenching. Three commercially available steroid hormone drugs, namely, norethindrone, norethindrone acetate, and ethisterone, were weaker than NET-EN in terms of binding capability with HSA. Displacement experiments demonstrated that similar to progesterone, the binding site of NET-EN was mainly located in site 1 of HSA. A circular dichroism (CD) study showed that NET-EN had a minimal effect on the local conformation of the HSA molecule. This study provided useful information for the better understanding and use of NET-EN.
