Catalyzes the condensation of the acetyl group of acetyl coenzyme A (acetyl-CoA) with oxaloacetate to form citrate. This enzyme is highly Re-face stereospecific with respect to the C-2 of oxaloacetate. acetyl-CoA + H2O + oxaloacetate = citrate + CoA + H(+) Inhibited by citrate and under aerobic conditions. Belongs to the alpha-IPM synthase/homocitrate synthase family.