56.
The title dipeptide {systematic name: (
S)‐2‐[(
S)‐2‐azaniumylbutanamido]‐3‐hydroxypropanoate}, C
7H
14N
2O
4, was synthesized in the anticipation that it would form nanoporous crystals with hexagonal symmetry. Single‐crystal X‐ray diffraction analysis showed that it had instead adopted a unit cell in the space group
I4, similar to L‐alanyl‐L‐alanine [Fletterick, Tsai & Hughes (1970).
J. Phys. Chem. 75 , 918–922]. The resulting packing arrangement has a high density for a peptide (1.462 Mg m
−3), which is rendered possible by extensive disorder over two positions for the ethyl side chain of the 2‐aminobutyric acid fragment and over three positions for the serine side chain.<!?tpb=17.5pt>
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