Imidazo[2,1-f][1,2,4]triazin-4-amine derivatives as TLR7 agonist

A compound of Formula (II),

• or a pharmaceutically acceptable salt thereof, or a stereoisomer thereof, wherein
• R1 is —OR1a or —NHR1a, wherein R1a is a branched —C4-8alkyl, wherein the branched substituent is at the alpha position with respect to the oxygen or nitrogen atom;
• Ring A is pyridyl;
• Het is piperidinyl or piperazinyl;
• R5 is C1-8 alkyl;
• p is 0 or 1;
• R6c is hydrogen, —COR6d, or C1-8 alkyl, wherein the C1-8 alkyl is optionally substituted with one, two or three substituents R6g;
• R6d is C1-8 alkyl, wherein the C1-8 alkyl is optionally substituted with one or two or three substituents R6g;
• R6g, at each occurrence, is independently —OR6h, —SR6h, or —NR6hR6i,
• R6h and R6i are independently hydrogen or C1-8 alkyl, wherein the C1-8 alkyl is optionally substituted with a substituent selected from hydroxyl or C1-8 alkylamino.