(2S,5R,6S)-6.beta.-Bromo-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]hepta ne-2-carboxylic acid, S,S-dioxide, physiologically acceptable salts thereof and readily hydrolyzable ester thereof inhibit the action of the .beta.-lactamase enzyme RTEM.

BACKGROUND OF THE INVENTION 
Bacteria that are normally susceptible to attack by .beta.-lactam 
antibiotics can develop a resistance to such attack by the production of a 
.beta.-lactamase enzyme. These enzymes catalyze the hydrolysis of the 
lactam ring of a .beta.-lactam antibiotic to a .beta.-amino acid 
derivative, which is not active against bacteria. 
One .beta.-lactamase enzyme is the RTEM enzyme. The RTEM enzyme is of 
plasmid origin and is said to be the most widely distributed 
.beta.-lactamase among the enteric gram-negative bacteria; see, Fisher et 
al., Annual Reports in Medicinal Chemistry, 13:239 (1978). The RTEM enzyme 
is capable of transferring into bacteria that are susceptible to 
.beta.-lactam antibiotics and rendering the organism resistant to these 
drugs; this ability to transfer from organism to organism, of course 
compounds the problem of the RTEM enzyme. This can be seen most clearly in 
the development recently of an ampicillin-resistant strain of N. 
gonorrhoeae. 
Two approaches have been followed in the search for a way to overcome, or 
at least minimize, the effects of .beta.-lactamases. The first is the 
synthesis of novel .beta.-lactam antibiotics which are stable against 
.beta.-lactamases. These efforts have enjoyed some success; however, the 
resistant derivatives synthesized seem to have a lower degree of 
antibacterial activity than the non-resistant analogs. The second approach 
comprises the use of a compound which inhibits the action of 
.beta.-lactamase enzymes on the lactam ring of a .beta.-lactam antibiotic. 
These .beta.-lactamase inhibitors are used in conjunction with the 
.beta.-lactam antibiotics. 
RELATED APPLICATION 
U.S. Patent application Ser. No. 968,539, filed Dec. 11, 1978, discloses 
that 
(2S,5R,6S)-6.alpha.-bromo-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]hep 
tane-2-carboxylic acid, S,S-dioxide, salts thereof, and readily 
hydrolyzable esters thereof, are inhibitors of the .beta.-lactamase enzyme 
RTEM. 
BRIEF DESCRIPTION OF THE INVENTION 
(2S,5R,6S)-6.beta.-Bromo-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]hepta 
ne-2-carboxylic acid, S,S-dioxide, salts thereof, and readily hydrolyzable 
esters thereof, are inhibitors of the .beta.-lactamase enzyme RTEM. This 
invention is directed to the above-named novel sulfone compound, to 
compositions comprising at least one of the above-named compounds in 
combination with a .beta.-lactam antibiotic susceptible to degradation by 
the RTEM enzyme, and to a method of inhibiting the action of the 
.beta.-lactamase enzyme RTEM on the .beta.-lactam antibiotic by the use of 
one of the above-named compounds. 
DETAILED DESCRIPTION OF THE INVENTION 
The novel compound of this invention, 
(2S,5R,6S)-6.beta.-bromo-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]hept 
ane-2-carboxylic acid, S,S-dioxide, salts thereof, and readily hydrolyzable 
esters thereof, can be obtained using 6,6-dibromopenicillanic acid as a 
starting material. 6,6-dibromopenicillanic acid is known in the art; see, 
for example, Clayton, J. Chem. Soc. (C), 2123 (1969). 
The carboxyl group in 6,6-dibromopenicillanic acid must be protected prior 
to the reduction of the molecule. This can be accomplished by reaction of 
the acid with a bulkyl ester group. The benzhydryl group has been found to 
be an effective protecting group, which can be cleaved without effecting 
the rest of the molecule. The benzhydryl ester can be formed by reacting 
the acid with diphenyldiazomethane in an organic solvent, e.g., ethyl 
acetate. 
Treatment of the benzhydryl ester of 6,6-dibromopenicillanic acid with a 
reducing agent, e.g., tri-n-butyl tin hydride, yields the benzhydryl ester 
of a 6.beta.-bromopenicillanic acid. 
Oxidation of 6.beta.-bromopenicillanic acid, benzhydryl ester yields the 
corresponding sulfone. The oxidation can be accomplished using any of the 
methods known to be useful for oxidizing a sulfur atom. Exemplary of the 
oxidizing agents which can be used are metachloroperbenzoic acid, hydrogen 
peroxide, potassium permanganate, etc. The oxidation reaction can be run 
in an organic solvent, e.g., ethyl acetate, or in water containing a 
miscible organic solvent, e.g., dioxane. Reaction temperature is not 
critical, and the reaction is conveniently run at room temperature. 
Alternative methods for the production of the products of this invention 
are available. For example, (2S, 5R, 
6S)-6.beta.-bromo-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo [3.2.0] 
heptane-2-carboxylic acid, S,S-dioxide can be obtained by first cleaving 
the ester group from 6.beta.-bromopenicillanic acid benzhydryl ester and 
then oxidizing the resulting acid. 
Physiologically acceptable salts of 
(2S,5R,6S)-6.beta.-bromo-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]-hep 
tane-2-carboxylic acid, S,S-dioxide are readily obtained using conventional 
techniques and are useful as .beta.-lactamase inhibitors. Exemplary of the 
salts specifically contemplated are those formed with a metal ion, e.g., 
alkali metal ions or alkaline earth metal ions, or amine salt ions. 
Readily hydrolyzable esters of 
(2S,5R,6S)-6.beta.-bromo-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo-[3.2.0]hep 
tane-2-carboxylic acid, S,S-dioxide are easily obtained using conventional 
techniques and are useful as .beta.-lactamase inhibitors. Exemplary of the 
ester groups which are readily hydrolyzed in vivo are those having the 
structural formula --CH(Y)--O--CO--alkyl, wherein Y is hydrogen or alkyl, 
e.g., acetoxymethyl and pivaloyloxymethyl; methoxymethyl; and 
isobenzofuranyl. 
As discussed above, under the heading "Background of the Invention", the 
RTEM enzyme is a .beta.-lactamase enzyme that catalyzes the hydrolysis of 
the lactam ring of a .beta.-lactam antibiotic yielding a derivative which 
is not active against bacteria. The treatment of a mammalian host with a 
.beta.-lactam antibiotic susceptible to degradation by the RTEM enzyme can 
be made more effective by the administration of 
(2S,5R,6S)-6.beta.-bromo-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]hept 
ane-2-carboxylic acid, S,S-dioxide, or a physiologically acceptable salt 
thereof, or a readily hydrolyzable ester thereof, in conjunction with the 
antibiotic. A compound of this invention can be administered 
simultaneously with a .beta.-lactam antibiotic or separately. 
Compositions comprising an RTEM enzyme inhibitor of this invention and a 
.beta.-lactam antibiotic susceptible to degradation by the RTEM enzyme are 
within the scope of this invention. The weight ratio of inhibitor to 
antibiotic can be from about 1:10 to 10:1, preferably from about 1:3 to 
3:1. Formulation of these compositions can be accomplished using 
conventional techniques, e.g., in powder form for reconstitution with a 
sterile vehicle for injection in solution; in suspension for oral 
administration; or the like. The compositions will preferably be 
formulated for administration in the manner conventionally used for 
administration of the antibiotic. 
Many of the known .beta.-lactam antibiotics have been shown to be 
susceptible to degradation by the RTEM enzyme. Current thinking (see, for 
example, Sykes et al., J. of Antimic Chemotherapy, 2,115 (1976) is that 
most of the penicillin antibiotics are susceptible (although to varying 
degrees) to degradation by the RTEM enzyme. Exemplary penicillins are 
ampicillin, amoxicillin, penicillin V, penicillin G, carbenicillin and 
sulbenicillin. The cephalosporins are not as susceptible as the 
penicillins to degradation by the RTEM enzyme; cephaloridine and 
cephalothin are exemplary of cephalosporins that are susceptible to 
degradation by the RTEM enzyme.