Here are some very general principles. Some amino acids are glycogenic, only two are ketogenic (leucine and lysine), and some are both glycogenic and ketogenic. The carbon skeletons of glycogenic amino acids can be made into pyruvate or oxaloacetate, either of which can be converted by liver into glucose via gluconeogenesis. Ketogenic amino acids can be turned into ketone bodies but not into glucose
Under starvation conditions, the brain uses a mixture of glucose and ketone bodies for fuel, in contrast to its otherwise strong preference for glucose.