This paper addresses the leader-follower synchronization problem of uncertain networked Euler-Lagrange systems under directed interconnection graphs in the presence of communication constraints. We 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. The information exchange between all systems in the network is assumed to be discrete in time, intermittent, and subject to irregular communication delays and possible packets dropouts. It is shown that leader-follower synchronization is reached for arbitrary characteristics of the communication process provided that the directed interconnection graph contains a spanning tree. Simulation results are given to illustrate the effectiveness of the proposed control scheme.