Catalyzes the condensation of pyruvate and acetyl-coenzyme A to form (R)-citramalate. acetyl-CoA + H2O + pyruvate = (3R)-citramalate + CoA + H(+) Amino-acid biosynthesis; L-isoleucine biosynthesis; 2-oxobutanoate from pyruvate: step 1/3. Homodimer. Belongs to the alpha-IPM synthase/homocitrate synthase family.