(2S,3R)-diaminobutanoate => (2S,3S)-diaminobutanoate
(2s,3r)-diaminobutanoate => (2s,3s)-diaminobutanoate
(2S,3R)-diaminobutanoate => (2S,3S)-diaminobutanoate
(2s,3r)-diaminobutanoate => (2s,3s)-diaminobutanoate