Country Life DL Phenylalanine with Vitamin B-6, is a 50/50 ratio of both the D and the L forms of phenylalanine. Phenylketonurics should avoid DL-Phenylalanine. Vitamin B-6 aids in the utilization of Phenylalanine. L-phenylalanine (LPA) serves as a building block for the various proteins that are produced in the body.