The present invention provides methods for identifying (3-amino-2-oxo-azetidin-1-yl) acetic acid derivatives with anti-PBP2a activity. The method involves the selection of RNA biocatalysts that promote the formation of (3-amino-2-oxo-azetidin-1-yl) acetic acid derivatives with anti-PBP2a activity from component reactants. The invention also provides novel (3-amino-2-oxo-azetidin-1-yl) acetic acid derivatives with anti-PBP2a activity identified by these methods. The invention also provides RNA biocatalysts that are capable of catalyzing the formation of (3-amino-2-oxo-azetidin-1-yl) acetic acid derivatives from component reactants.