主权项 |
1. A compound of the formula: or a salt thereof, wherein: R1 is selected from 2-methylpropyl, tert-butyl, 2-methylbutyl, 2,2-dimethylpropyl, 2-methylbut-2-yl, cyclobutylmethyl, cyclopropylmethyl, cyclopentylmethyl, isopropyl, 1-methylcyclohexyl, 1-methylcyclopentylmethyl, 2-cyclopropylpropyl, 1-methylcyclobutyl, cyclopentyl, 2,3-dimethylbutan-2-yl, 1-ethylcyclobutylmethyl, 1-methylcyclopentyl, 2-cyclopropylpropan-2-yl, cyclobutyl, 1-methylcyclobutylmethyl, 1-(trifluoromethyl)cyclobutyl, 1-ethylcyclobutyl, (2H3)methyl(2H6)propyl and 2-methylpentan-2-yl; R2 is selected from hydrogen, methyl, ethyl and isopropyl; or R1 and R2 together with the nitrogen atom to which they are attached form a non-aromatic heterocyclic group of four to nine ring members, wherein the heterocyclic ring may optionally contain a second heteroatom selected from O, N and S and oxidised forms thereof; and wherein the heterocyclic ring may optionally be substituted with one to six more substitutents selected from C1-2 alkyl; fluorine; and cyano; R3 is selected from hydrogen; fluorine; cyano; methoxy and methyl; and R4 is selected from methyl, ethyl, ethynyl and 1-propynyl. |