Penam sulfones and β-lactamase inhibition: SA2-13 and the importance of the C2 side chain length and composition

PLoS One. 2014 Jan 16;9(1):e85892. doi: 10.1371/journal.pone.0085892. eCollection 2014.


β-Lactamases are the major reason β-lactam resistance is seen in Gram-negative bacteria. To combat this resistance mechanism, β-lactamase inhibitors are currently being developed. Presently, there are only three that are in clinical use (clavulanate, sulbactam and tazobactam). In order to address this important medical need, we explored a new inhibition strategy that takes advantage of a long-lived inhibitory trans-enamine intermediate. SA2-13 was previously synthesized and shown to have a lower k(react) than tazobactam. We investigated here the importance of the carboxyl linker length and composition by synthesizing three analogs of SA2-13 (PSR-4-157, PSR-4-155, and PSR-3-226). All SA2-13 analogs yielded higher turnover numbers and k(react) compared to SA2-13. We next demonstrated using protein crystallography that increasing the linker length by one carbon allowed for better capture of a trans-enamine intermediate; in contrast, this trans-enamine intermediate did not occur when the C2 linker length was decreased by one carbon. If the linker was altered by both shortening it and changing the carboxyl moiety into a neutral amide moiety, the stable trans-enamine intermediate in wt SHV-1 did not form; this intermediate could only be observed when a deacylation deficient E166A variant was studied. We subsequently studied SA2-13 against a relatively recently discovered inhibitor-resistant (IR) variant of SHV-1, SHV K234R. Despite the alteration in the mechanism of resistance due to the K→R change in this variant, SA2-13 was effective at inhibiting this IR enzyme and formed a trans-enamine inhibitory intermediate similar to the intermediate seen in the wt SHV-1 structure. Taken together, our data reveals that the C2 side chain linker length and composition profoundly affect the formation of the trans-enamine intermediate of penam sulfones. We also show that the design of SA2-13 derivatives offers promise against IR SHV β-lactamases that possess the K234R substitution.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Substitution
  • Anti-Bacterial Agents / chemistry*
  • Bacterial Proteins / antagonists & inhibitors*
  • Bacterial Proteins / chemistry
  • Catalytic Domain
  • Crystallography, X-Ray
  • Heterocyclic Compounds, 2-Ring / chemistry*
  • Kinetics
  • Models, Molecular
  • Penicillanic Acid / analogs & derivatives*
  • Penicillanic Acid / chemistry
  • Protein Binding
  • Structure-Activity Relationship
  • Sulfones / chemistry*
  • Tazobactam
  • Thiazolidines / chemistry*
  • beta-Lactam Resistance
  • beta-Lactamase Inhibitors*
  • beta-Lactamases / chemistry
  • beta-Lactamases / genetics


  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Heterocyclic Compounds, 2-Ring
  • PSR-3-226
  • SA2-13 compound
  • Sulfones
  • Thiazolidines
  • beta-Lactamase Inhibitors
  • Penicillanic Acid
  • beta-lactamase PIT-2
  • beta-Lactamases
  • Tazobactam