Cognitive radios CR have the ability to dynamically adapt to local spectrum availability. In a multi-hop wireless network comprised of CR-enabled devices, Medium Access Control (MAC) layer scheduling for data communication involves assignment of timeslots and channels to either links or nodes in the network. The number of channels available and the channel identities vary from one node to another within the CR network. This is in contrast to the existing use of multiple channels where all the nodes have the same set of channels available (for example in IEEE 802.11 networks). In this paper, we present an Integer Linear Programming (ILP) formulation for the MAC-layer scheduling problem and find an optimal schedule. We also propose a simple and efficient distributed heuristic for MAC-layer scheduling. Simulation results indicate that the proposed distributed heuristic provides near optimal schedule.