Interpreting the Stereochemistry of Phosphorus and Proving Commercial Success: How Gilead’s Nucleoside Phosphoramidate Prodrug Patent “Captured” Sofosbuvir and Survived Invalidation

In pharmaceutical patent disputes, claim interpretation can be decisive because it defines the claimed subject matter against which novelty and inventive step are assessed. A single stereochemical notation in a structural formula may determine whether a patented claim covers a commercially successful drug worth billions of dollars. The dispute in the Gilead Sciences Inc. (hereinafter “Gilead Sciences”) patent (“Nucleoside Phosphoramidate Prodrug patent”) centers on whether the solid line at the chiral phosphorus atom denotes a specific stereochemical configuration or left the stereochemistry undefined (Figure 1). With the marketed product being the single Sₚ diastereomer, the interpretation of that solid line determines whether the product is covered by the granted claim..…