The idea of synthesizing state-based models from scenario-based interaction specifications has received much attention in recent years. The synthesis approach not only helps to significantly reduce the effort of system construction, but it also provides a bridge over the gap between requirements and implementation of systems. However, the existing synthesis techniques only focus on generating (global or local) state machines from scenario-based specifications, while the coordination among the behavior alternatives of services/components in the systems is not considered. In this paper we propose a novel synthesis technique, which can be used to generate constraint automata specification for connectors from scenario specifications. Inspired by the way UML2.0 sequence diagrams can be algebraically composed, we define an algebraic framework for building constraint automata by exploiting the algebraic structure of UML sequence diagrams.