Cyclobutyl-Containing Rigid Analogues of Threonine: Synthesis and Physical Chemical Properties

Hitherto
unknown cis- and trans-1-amino-3-hydroxy-3-methylcyclobutanecarboxylic
acids were synthesized
in multigram scale. The obtained compounds can be considered as achiral
conformationally restricted analogues of threonine with fixed spatial
orientation of functional groups. pKa values
are noticeably different for both amino acids. According to the X-ray
data the cyclobutane rings in both compounds are almost planar (the
corresponding torsion angles are below 7°).