In this paper we study the leader-follower synchronization problem of networked uncertain Euler-Lagrange systems under directed interconnection graphs. We first consider the case of ideal communication between agents and present an adaptive distributed control algorithm such that a group of Euler-Lagrange systems asymptotically synchronize their states to those of a dynamic leader with a time-varying trajectory. Then, we propose a modified design that achieves the same control objective under the assumption of intermittent discrete-time communication in the presence of varying communication delays and possible packet dropout. It is shown that leader-follower synchronization is achieved under sufficient conditions that can be realized uniformly of the interconnection topology between agents for a given characteristics of the communication process. Simulation results are given to illustrate the effectiveness of the proposed control scheme.