This invention provides biphenyl derivatives of formula I:
1
wherein R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, W, a, b and c are as defined in the specification, or a pharmaceutically acceptable salt or solvate or stereoisomer thereof. The biphenyl derivatives of this invention possess both &bgr;
2
adrenergic receptor agonist and muscarinic receptor antagonist activity and therefore, such biphenyl derivatives are useful for treating pulmonary disorders, such as chronic obstructive pulmonary disease and asthma.