J. Med. Chem. 2003, 46, 4173-4181
4173
Soft Antimicrobial Agents: Synthesis and Activity of Labile Environmentally Friendly Long Chain Quaternary Ammonium Compounds Thorsteinn Thorsteinsson,†,‡ Ma´r Ma´sson,† Karl G. Kristinsson,§ Martha A. Hja´lmarsdo´ttir,§ Hilmar Hilmarsson,| and Thorsteinn Loftsson*,† Faculty of Pharmacy, University of Iceland, Hagi, Hofsvallagata 53, IS-107 Reykjavik, Iceland, Decode Genetics Inc., Reykjavik, Iceland, Department of Clinical Microbiology, Landspitali University Hospital, IS-101 Reykjavik, Iceland, and Institute of Biology, University of Iceland, Hagi, Hofsvallagata 53, IS-107 Reykjavik, Iceland Received March 26, 2003
A series of soft quaternary ammonium antimicrobial agents, which are analogues to currently used quaternary ammonium preservatives such as cetyl pyridinium chloride and benzalkonium chloride, were synthesized. These soft analogues consist of long alkyl chain connected to a polar headgroup via chemically labile spacer group. They are characterized by facile nonenzymatic and enzymatic degradation to form their original nontoxic building blocks. However, their chemical stability has to be adequate in order for them to have antimicrobial effects. Stability studies and antibacterial and antiviral activity measurements revealed relationship between activity, lipophilicity, and stability. Their minimum inhibitory concentration (MIC) was as low as 1 µg/mL, and their viral reduction was in some cases greater than 6.7 log . The structure-activity studies demonstrate that the bioactive compounds (i.e., MIC for Grampositive bacteria of 1000 32 8
a
Staphylococcus aureus ATCC 25923
MLC
MIC
>2000 64 >1000 32 16
15 2000 2 >2000 8 8 4 7.5 7.5 16 >2000 4 1 12800 >12800 >12800 >12800 >12800 4 1000 250 >12800
8 3200 200 >2000 100 >2000 8 8 62 64 >2000 16 4 12800 >12800 >12800 >12800 >12800 8 8 >1000 500 >12800
4 4 1 8 32 16 32 32 64
MLC
>2000 16 >1000 16 2
MIC
>2000 >2000 16 64 >1000 >1000 16 16 4 64 not determined 250 4 16 3200 3200 50 100 >2000 >2000 50 25 500 1000 1 32 2 500 16 62 60 250 16 500 >2000 >2000 4 125 1 250 12800 12800 >12800 >12800 >12800 >12800 12800 6400 >12800 >12800 4 125 4 1000 >1000 >1000 250 >1000 >12800 >12800 not determined 8 125 2 125 8 16 32 125 16 500 32 250 16 125 250 125 125 125
7.5 2000 2000 4 12800 >12800 12800 >12800 4 1000 250 >12800
16 8 4 16 125 16 32 32 64
Escherichia col ATCC 25922
2 2 1 8 8 4 8 16 32
Pseudomonas aeruginosa ATCC 27853
MLC
MIC
MLC
>2000 64 >1000 125 64
>2000 250 >1000 250 250
>2000 250 >1000 250 250
3200 400 >2000 100 1000 32 500 125 500 >2000 125 250 12800 >12800 >12800 12800 >12800 125 >2000 >1000 >1000 >12800
500 500 3200 3200 >2000 200 >2000 250 250 250 250 >2000 g2000 >2000 250 500 12800 >12800 >12800 6400 >12800 125 1000 >1000 >1000 >12800
1000 3200 3200 >2000 200 >2000 1000 250 250 g2000 >2000 250 500 12800 >12800 >12800 6400 >12800 125 >2000 >1000 >1000 >12800
125 250 64 125 500 500 250 250 250
500 250 64 500 g2000 g g2000 500 1000
1000 1000 64 500 g2000 g2000 g2000 1000 1000
3a ) Cetylpyridinium chloride and 5 ) benzalkonium chloride.
Table 3. Composition in Percentage for the Mixture Compounds 6a-f compound 6a 6b 6c 6d 6e 6f
3e
3g
3h
4b
4c
2b
2c
3w
3v
43.5 56.5 58.1 41.9 59.9 40.1 24.6 50.8 24.6 26.1 23.5 23.4 27.0 60.4 39.6 -
the synthesis, and they had negligible antibacterial activity (MIC > 250 µg/mL); therefore, the activity was due to the antibacterial properties of the compounds and not to that of impurities or degradation products. The long chain compounds 1b, 2,b, 2e, 3i, 3l, and 3m were able to inhibit bacterial growth and even kill some bacteria at as low concentration as 10 µg/mL. However, compounds 2c, 3e, 3g, 3h, 3p, 3k, 3o, 3v, 3w, 4b, and 4c were inhibitory at concentrations
