Dalfopristin (mesylate) is a streptogramin antibiotic and a 50S ribosome inhibitor [1][2].

Streptogramins are produced by a variety of Streptomyces sp as a mixture (ratio of 7:3) of two chemically unrelated compounds, type A and B. Dalfopristin, the type A Streptogramin, is often combined with type B streptogramin antibiotic, quinupristin, to produce Quinupristin-Dalfopristin Complex, known commercially as Synercid. Synercid is used to treat skin infections, and is also active against some Gram-negative and anaerobic bacteria [2][3].

The ribosome is composed of two ribonucleoprotein subunits, the 50S and 30S. The 50S ribosome inhibitors inhibited protein synthesis [2].

Dalfopristin is a cyclic polyunsaturated macrolactone that interferes with binding of tRNA substrates to both A- and P-sites [2]. Dalfopristin blocked the access of peptidyl-tRNAs to the ribosome and peptidyltransferase elongation reaction in bacteria [1]. quinupristin and dalfopristin acted synergistically to kill Gram-positive bacteria, as well as some Gram-negative and anaerobic bacteria [2][3]. Dalfopristin hydrolyzed rapidly to virginiamycin M under physiological conditions.

References:
[1].  Kohanski MA, Dwyer DJ, Collins JJ. How antibiotics kill bacteria: from targets to networks. Nat Rev Microbiol. 2010 Jun;8(6):423-35.
[2].  Wilson DN. The A-Z of bacterial translation inhibitors. Crit Rev Biochem Mol Biol. 2009 Nov-Dec;44(6):393-433.
[3].  Noeske J, Huang J, Olivier NB, et al. Synergy of streptogramin antibiotics occurs independently of their effects on translation. Antimicrob Agents Chemother. 2014 Sep;58(9):5269-79.