We propose a new distributed algorithm for optimal channel assignment in WLANs with multiple access points, applying a novel formulation for wireless networks based on Distributed Constraint Optimization Problem (DCOP). The DCOP approach allows to model a wide variety of distributed reasoning tasks of multi-agent applications. The proposed strategy is derived from a polynomial-space algorithm for DCOP named ADOPT, which is guaranteed to find the global optimal solution while allowing agents to execute asynchronously and in parallel. Our proposed algorithm, denoted DCAA-O, allows a group of APs to coordinate themselves in order to find the optimal channel allocation solution which minimizes the network interference. The algorithm performance is evaluated in terms of the required number of transmitted control messages among APs. It is shown that DCAA-O outperforms a recently proposed channel assignment strategy for WLANs.