Compounds for the treatment of sars

A compound of the formula (I):

• or a pharmaceutically acceptable salt thereof, wherein:
• R1 is alkyl, —O-alkyl, -heterocyclyl, —O-heterocyclyl, —O-alkylene-heterocyclyl, —O-alkylene-aryl, -alkylene-heterocyclyl, —N(Ra)alkyl, —N(Ra)heterocyclyl, alkylene-O-heterocyclyl, alkylene-O-aryl, or -alkylene-N(H)C(O)CF3;
• each of which can be substituted with any suitable substituent, including halo, alkyl, alkoxy, alkoxyalkyl, and aminoalkyl;
• R2 is alkyl, aryl, substituted aryl;
• R3 is heterocyclyl or cycloalkyl;
• R4 is H, alkyl or alkenyl;
• and
• Ra is H or alkyl,
• or a pharmaceutically acceptable salt thereof.