Chiral Analysis of the Key Intermediates of Tenofovir Alafenamide Fumarate

Abstract ( R )-Tenofovir phenyl ester (( R ) -1 ) and ( R )-tenofovir diphenyl ester (( R ) -2 ) are key intermediates for the practical synthesis of tenofovir alafenamide fumarate, which is a mainstay antiretroviral for the treatment of chronic hepatitis B and HIV-1 infections. This article deals with the chiral analysis of ( R )- 1 and ( R )- 2 against their respective optical impurity ( S )-tenofovir phenyl ester (( S )- 1 ) and ( S )-tenofovir diphenyl ester (( S )- 2 ) using a polysaccharide-coated chiral stationary phase (CSP) by normal-phase high-performance liquid chromatography (HPLC). To this end, a chiral synthetic strategy for ( S )- 2 was efficiently executed capitalizing on a classical Mitsunobu reaction to stereospecifically invert the configuration of chiral carbon in readily accessible ( R )-HPA (( R )- 4 ) to deliver ( S )-HPA (( S )- 4 ), from which ( S )--tenofovir ((S)- 3 ) was in turn prepared and further transformed into ( S )- 2 . With reference substance ( S )- 2 in hand, a chiral analytical method for ( R )- 2 using Chiralpak AD-H as CSP by normal-phase HPLC has been developed and validated. The validation results indicated that this chiral analytical method has been achieved with satisfactory separation effect, high sensitivity, and good precision and accuracy, and thus can be deployed for the determination of optical impurities in samples of ( R )- 1 (via derivation to ( R )- 2 ) and ( R )- 2 .