The invention provides compounds of formula I and pharmaceutically acceptable salts thereof processes for their preparation, pharmaceutical compositions containing them and their use in therapy. Compounds of formula I wherein R¹ is amino and C_5-6 heteroaryl; R² is H, CN, amino, C_1-6 alkyl, etc.; R³ is (un)saturated 3- to 10-membered ring; n is 0, 1, 2, and 3; each R⁴ is independently C_1-6 alkyl; X is CO, CONH, CO(CR¹⁷)_y(CR¹⁸)_x; x and y are independently 0 and 1, provided that the sum of x + y is at least 1; R¹⁷ and R¹⁸ are H and C_1-6 alkyl; R¹⁷R¹⁸ may be taken together ro form a cyclopropyl ring; and pharmaceutically acceptable salts thereof, are claimed. Example compound II was prepared by N-acylation of 1-{2-methyl-5H,6H,7H-pyrrolo[3,4-d]pyrimidin-4-yl}azetidine dihydrochloride with 4-chloro-2-methylbenzoic acid. The invention compounds were evaluated for their M2 and M4 receptor modulatory activity. From the assay, it was determined that compound II exhibited EC₅₀ value of 0.56 μM and relative efficacy of 86 %.