Are the known Δ2‐cephems inactive as antibiotics because of an unfavourable steric orientation of their 4α‐carboxylic group? Synthesis and biology of two Δ2‐cephem‐4β‐carboxylic acids

Abstract
Two representatives of the yet unknown type of Δ2‐cephem‐4β‐carboxylic acids were prepared. Contrarily to the prediction based on the activity model of Cohen, both acids proved inactive as antibiotics. Possible reasons for this discrepancy are briefly discussed.