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- H2N−CH2−COOHH_{2} N-C H_{2}-C O O H
- H2N−CH2−CH2−COOHH_{2} N-C H_{2}-C H_{2}-C O O H
- HOOC−CH2CH(NH2)COOHH O O C-C H_{2} C H\left(N H_{2}\right) C O O H
- CH3−CH(NH2)−COOHC H_{3}-C H\left(N H_{2}\right)-C O O H