Prodrugs of carbonic anhydrase inhibitors

Prodrugs are prepared of the carbonic anhydrase inhibitors 2-benzothiazolesulfonamide, hydroxymethazolamide, and dichlorphenamide. The prodrugs link a water soluble compound to the pharmacologically active carbonic anhydrase inhibitor through an enzymatically or hydrolytically degradable bond.

EXAMPLE 1 
Synthesis of 6-[.beta.-glucopyranosyl)oxyethoxy]-2-benzothiazolesulfonamide 
A solution of acetobromoglucose (4.93 g.; 12.0 mmole), 
6-[2'-hydroxyethoxy]-2-benzothiazolesulfonamide (2.74 g.; 10.0 mmole), and 
2,4,6-collidine (1.09 g.; 9.00 mmole) in dry tetrahydrofuran (50 mL) were 
added at -25.degree. C. to a suspension of silver triflate (3.60 g.; 14.0 
mmole) in dry tetrahydrofuran over a period of 30 minutes. The reaction 
mixture was stirred overnight at room temperature. Collidine (2 mL) was 
added and the mixture filtered through paper. The filtrate was washed with 
aqueous sodium thiosulfate solution, the organic layer separated, and 
evaporated to dryness at reduced pressure. The solid residue was 
chromatographed on a silica gel column (300 g.) and eluted with 
chloroform. The product fractions (UV light and charring positive) were 
combined and evaporated to dryness at reduced pressure. 
The unpurified 
6-[2'-(2",3",4",6"-tetra-O-acetyl-.beta.-glucopyranosyl)oxyethoxy]-2-benzo 
thiazolesulfonamide (3.02 g.; 5.00 mmole) was dissolved in anhydrous 
diethyl ether (100 mL) and combined with cold (0.degree. C.) saturated 
methanolic ammonia (100 mL) and stirred overnight with the temperature 
rising to room temperature over a six hour period. The solution was 
evaporated to dryness at reduced pressure and chromatographed on a silica 
gel column (150 g.) and eluted with chloroform/methanol (9.1). The product 
fractions (UV light and charring positive) were combined and evaporated to 
dryness at reduced pressure, and lyophilized to yield 
6-[.beta.-lucopyranosyl)oxyethoxy]-2-benzothiazolesulfonamide. The product 
conformed to accepted standards of purity and its structural assignment 
verified by standard spectroscopic methods (mass spec,.sup.13 C and .sup.1 
H nuclear magnetic resonance). 
EXAMPLE 2 
Reduction in IOP Following Topical Application of the Compound of Example 1 
to Dutch Belt Rabbit Eyes 
Healthy, Dutch Belt rabbits, accustomed to the experimental procedure, 2-3 
months old, of either sex and weighing about 3-4 pounds were placed in 
restraining boxes. Intraocular pressure (IOP) was measured using a 
pneumatonograph (Digilabs Model 30D, Cambridge, Mass.) and 1-2 drops of 
0.5% proparacaine hydrochloride for anesthesia. IOP is measured in both 
eyes. The drug of Example 1 is dissolved in a 3% carbomer 940 vehicle 
(Carbopol 940, B. F. Goodrich, Cleveland, Ohio) and instilled (50 .mu.L) 
into the lower conjunctival sac of the right eye only. 
The "IOP recovery rate assay" as reported by Vareilles and Lotti 
(Ophthalmic Res., 13, 72-79, 1981) is used. In this assay 20% sodium 
chloride solution is infused into the marginal ear vein for 10 minutes at 
a rate of 1 mL/min. This procedure was altered by infusing 10% sodium 
chloride solution for 15 minutes at a rate of 1 mL/min. to minimize 
vascular damage IOP is measured just prior to beginning the infusion and 
again at 15, 25, 35, 45, 60, 75, 90, 120, 150, 180, and 210 minutes. 
The hypertonic sodium chloride solution causes a decline in IOP which then 
recovers at a rate dependent on the activity of carbonic anhydrase. IOP 
gradually returns to normal at a constant rate but much more slowly if a 
carbonic anhydrase inhibitor is present in the eye in sufficient 
concentration. The return to normal is measured from the positive linear 
slope which begins at about 45-60 minutes after starting the infusion. The 
test drug (3% drug in carbomer vehicle) is administered 60 minutes before 
the start of the sodium chloride solution infusion. Control animals are 
given vehicle without drug. 
Results are expressed as mean values .+-. standard deviation of the slopes 
representing recovery of IOP (mm Hg/min.): 
##EQU1## 
The topically treated rabbit eyes show a statistically slower (p&lt;0.05) 
recovery rate to normal IOP values when compared to control eyes which 
only received vehicle. This indicates the drug works. 
Other satisfactory results can also be achieved when the 
2-benzothiazolesulfonamide carbonic anhydrase inhibitor of the Examples 1 
and 2 is substituted with methazolamide/acetazolamide analogs and 
dichlorphenamide analogs, in that water solubility is increased, and 
carbonic anhydrase inhibition is still maintained at effective levels. 
This indicates degradation of the linkage between the water soluble 
carrier and the carbonic anhydrase inhibitor by enzymes within the eye 
such that the carbonic anhydrase inhibitor continues to exhibit CAI 
activity. 
In these and other examples, as in the parent case, the amount of the 
carbonic anhydrase inhibitor active used in the composition should be from 
about 0.25% by weight to about 5% by weight of an eye drop test 
composition, preferably from about 0.5% by weight to about 2.0% by weight. 
The important point is not the dose amount, but simply that it be an 
effective carbonic anhydrase inhibiting amount, and yet not such a great 
amount that side effects will be achieved. Generally, amounts within the 
range specified are satisfactory. 
The diluent for the eye drop composition may be an isotonic eye treatment 
carrier buffered to a pH of from about 4.0 to about 8.0, and typically it 
will contain small amounts of conventional wetting agents and 
antibacterial agents. The preferred pH is within the range of from about 
6.8 to about 7.8. Antibacterial agents, where they are included may be 
within the range of from about 0.004% by weight to about 0.02% by weight 
of the composition.