2-phenylimidazo[4,5-c]pyridines

A compound of the formula ##STR5## or its pharmaceutically acceptable salt, wherein R.sub.1 is hydrogen, C.sub.1 -C.sub.4 alkyl, or chloro;

• R.sub.2 and R.sub.3 each are independently hydrogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, allyloxy, C.sub.1 -C.sub.4 alkylthio, C.sub.1 -C.sub.4 alkylsulfinyl, C.sub.1 -C.sub.4 alkylsulfonyl, hydroxy, halo, cyano, nitro, amino, mono- or di-(C.sub.1 -C.sub.4 alkyl)amino, trifluoromethyl, or Z-Q-substituted C.sub.1 -C.sub.4 alkoxy, wherein Q is oxygen, sulfur, sulfinyl, sulfonyl, or a bond, and Z is C.sub.1 -C.sub.4 alkyl, phenyl, or phenyl substituted with a group selected from halo, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, hydroxy, nitro, amino, C.sub.1 -C.sub.4 alkylthio, C.sub.1 -C.sub.4 alkylsulfinyl, or C.sub.1 -C.sub.4 alkylsulfonyl;
• and
• R.sub.4 is hydrogen, C.sub.1 -C.sub.4 alkyl, or C.sub.1 -C.sub.4 alkoxy;
• with the provisions that:
• (a) if R.sub.1 and two of R.sub.2, R.sub.3, and R.sub.4 are all hydrogen, the other of R.sub.2, R.sub.3, and R.sub.4 is not hydrogen, halo, hydroxy, nitro, amino, di-(C.sub.1 -C.sub.2 alkyl)amino, or C.sub.1 -C.sub.2 alkoxy;
• (b) if R.sub.1 and one of R.sub.2, R.sub.3, and R.sub.4 are both hydrogen, and another of R.sub.2, R.sub.3, and R.sub.4 is C.sub.1 -C.sub.2 alkoxy, the other of R.sub.2, R.sub.3, and R.sub.4 is not hydroxy or C.sub.1 -C.sub.2 alkoxy;
• (c) if R.sub.1 is chloro and two of R.sub.2, R.sub.3, and R.sub.4 are both hydrogen, the other of R.sub.2, R.sub.3, and R.sub.4 is not hydrogen, halo, C.sub.1 -C.sub.2 alkyl, or nitro;
• and
• (d) if R.sub.1 is chloro and R.sub.4 is hydrogen, R.sub.2 and R.sub.3 may not both be nitro.