In this paper, we present a low-power architectural synthesis system (LOPASS) for field-programmable gate-array (FPGA) designs with interconnect power estimation and optimization. LOPASS includes three major components: 1) a flexible high-level power estimator for FPGAs considering the power consumption of various FPGA logic components and interconnects; 2) a simulated-annealing optimization engine that carries out resource selection and allocation, scheduling, functional unit binding, register binding, and interconnection estimation simultaneously to reduce power effectively; and 3) a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cofamily</i> -based register binding algorithm and an efficient port assignment algorithm that reduce interconnections in the data path through multiplexer optimization. The experimental results show that LOPASS produces promising results on latency optimization compared to an academic high-level synthesis tool <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SPARK</i> . Compared to an early commercial high-level synthesis tool, namely, Synopsys <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Behavioral Compiler</i> , LOPASS is 61.6% better on power consumption and 10.6% better on clock period on average. Compared to a current commercial tool, namely, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Impulse C</i> , LOPASS is 31.1% better on power reduction with an 11.8% penalty on clock period.