The most toxic compounds is

ANS:B - phenylpyruvate

Phenylpyruvate is formed when phenylalanine loose its amino group. Accumulation of phenylalanine will increase the levels of phenylpyruvate and deprives the brain of alph ketoglutarate which will cause the brain to shut the TCA cycle and hence aerobic respiration. This condition is known as phenylketonuria victims start to have mental issues.

It can again inhibit the expression of tyrosinase enzyme leading to deficiency of pigmentation.