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The influence of chemical structure on fungal activity. III. Effect of o-chlorination on phenols
The Influence of Chemical Structure on Fungal Activity. III. Effect of o-Chlorination on Phenols’ Harold G. Shirk and Roland R. Corey, Jr.” of Deterioration Center, National Research Council, D. C.; and the Department of Bacteriology, University of Maryland, College Park, Maryland
From the Prevention Washington,
Received February 11, 1952 INTRODUCTION
The various isomeric forms of monochlorophenol, including its mono- and polyalkyl derivatives, have very often been included in the search for more efficient fungicides. Cooper and Woodhouse (I), Gersdorff and Smith (2), Gruenhagen, Wolf, and Dunn (3), Hatfield (4), Kuroda (5), and Woodward, Kingery, and Williams (6) have concluded that the paru-positioning of chlorine in phenol or its alkyl derivatives, in contrast to o&ho-positioning, produces more efficacious chemicals as regards their fungicidal activity. A similar generalization appears in the conclusions of Klarmann and his associates (7,8) who examined and compared the relationship between chemical constitution of aliphatic- and aromatic-substituted p- and o-chlorophenols and their germicidal potency. Despite this evidence it appeared desirable, for comparative purposes, to include the o-chlorophenol group of derivatives in the projected search for fungistatic agents. Two earlier papers in this series (10,ll) reported the relative inhibitory effectiveness of p-chlorophenols and the increased fungistatic potency imparted to phenols by para-chlorination. The present work, however, includes both a fungistatic assay of o-chlorophenols and a record of the effect produced by o&ho-chlorination of some alkylated 1 Reported in part before the Conference on Microbiological Deterioration at the Gordon Research Conferences, Am. Assoc. Advancement Sci., July-August, 1950, and sponsored by the Departments of Air Force, Army, and Navy under Contract N7onr-29127. *Present address: College of Agriculture, University of California, Davis, California. 417
418
HAROLD G. SHIRK AND ROLAND R. COREY, JR.
phenols. The results for some derivatives not previously referred to in the literature are included. Except for the systematic studies performed with a homologous series of o-chlorophenols by Klarmann et al. (7,8) and by Blicke and Stockhaus (9), alkyl derivatives of o-chlorophenol have not attracted too much attention as potential antimicrobial agents. METHOD The bioassay procedure employed for evaluating the fungistatic activity of the unhalogenated phenols and numerous o-chlorophenols included in this report was the same as described in the original report of this series by Shirk, Poelma, and Corey (10). RESULTS AND DISCUSSION
The dosage-response data in Table I depict the relative fungistatic efficiency for 17 phenols together with the potency registered for the companion o-chloro compounds. To facilitate evaluation of the effect induced by ortho-chlorination, the interpolated concentration values for each test agent which inflicted a 50% growth inhibitory response are given. In several cases when the lowest concentration (as shown in Table I), caused an inhibition greater than SO%, additional data, not shown here, were used to produce a valid interpolated concentration value. With the exception of phenol, p-cresol, and possibly 3,5-xylenol, the effect induced by ortho-chlorination added nothing to the fungistatic worth of the test compounds; in fact, with many alkylated derivatives chlorine introduction in the ortho-position detracted markedly from the effectiveness of the molecule in inhibiting Aspergillus niger growth. Phenols such as o-isopropyl-, o-phenyl-, o-cyclohexyland the dialkylated derivatives having one of its alkyls in the 6-position, while quite fungistatic in their unhalogenated state, suffered particular dimunition in activity by the introduction of chlorine into the remaining ortho-position. Even the ortho-introduction of chlorine in phenol derivatives devoid of substituents in the second ortho-position, as illustrated by the p-isopropyl-, p-tert-butyl-, p-nonyl-, and p-phenylphenol derivatives, produced compounds which possessed no greater activity than the unhalogenated phenols. Although the fungitoxic properties of p-cresol and phenol were increased an approximate two- to threefold by o&ho-chlorination (as determined by comparing concentrations inhibiting growth 50 %, see Table I), Shirk et al. (11) showed that para-substitution of the halogen
CHEMICAL
STRUCTURE
ON
TABLE Effect
--
of Some Substituted
Compound
Phenol o-Chlorophenol p-Cresol o-Chloro-p-cresol o-Cresol 6-Chloro-o-cresol p-Isopropylphenol o-Chloro-p-isopropylphenol o-Isopropylphenol 6-Chloro-o-isopropylphenol p-tert-Butylphenol o-Chloro-p-tert-butylphenol p-Nonylphenol o-Chloro-p-nonylphenol p-Phenylphenol o-Chloro-p-phenylphenol” o-Phenylphenol 6-Chloro-o-phenylphenol o-Cyclohexylphenol 6-Chloro-o-cyclohexylphenol 3,5-Xylenol o-Chloro-3,5-xylenol p-tert-Butyl-o-cresol 6-Chloro-p-fert-butyl-o-cresol 6-tert-Butyl-m-cresol o-Chloro-6-tert-butyl-m-cresol o-tert-Butyl-p-cresol 6-Chloro-o-tert-butyl-p-cresol 2,4-Diisopropylphenol 6-Chloro-2,4-diisopropylphenol 4,6-DCtert-butyl-m-cresol o-Chloro-4,6-di-tert-butyl-mcresol 2,CDiamylphenolb 6-Chloro-2,4-diamylphenolb
Phenols
FUNGAL
ACTIVITY.
I
and Their o-Chloro of A. niger
Derivatives
Percent inhibition of growth Concentration (10-a M) 5.0 2.5 1.0 10.0 7.5
7---40 33 36 29 58 47 33 25 38 32 100 82 Tr.” 82 79 69 24 19 Tr. Tr. Tr. 92 100 100 67 65 100 100 100 100 100 100 Tr. Tr. 100 100 Tr. 92 68 61 84 82 100 91 46 35 100 98 45 28 100 100 47 27 100 92 62 54 77 75 24 69 13
15 68 9
419
III
25 23 35 18 23 56 63 51 17 76 77 Tr. 63 Tr. 100 Tr. 92 100 87 46 61 69 18 81 15 82 18 76 47 69
10 15 23 12 9 32 32 29 12 40 46 Tr. 57 80 82 87 68 81 65 30 24 40 12 55 7 66 5 54 29 68
4 7 13 7 3 23 16 16 4 25 29 69 46 51 50 68 51 51 43 13 22 24 3 39 6 37 0 37 14 63
9 6 4 64 64 54 12 9 9
on the Growth
e;;g growth x lo-’
50% iki
45 14 18 8.5 18 17 4.5 4.0 5 25 3.5 3.0 0.75 1.50 1.0 1.0 0.8 1.0 1.0 1.4 5.5 4.5 3.5 10.5 2.3 12 1.5 12 2.2 6 >50 0.9 >lOO
Effect of o-chlorination on fungitoxicity
f + 0 0 Neg. 0 Neg. 0 Neg. Neg. + Neg. Neg. Neg. Neg.
Neg. Neg.
mDowicide 4, 85% o-Chloro-p-phenylphenol. b Mixture of secondary and tertiary amyl substituents. c Tr. = trace of mycelial development and growth noted but could not be measured accurately.
420
HAROLD
G. SHIRK
AND
ROLAND
R.
COREY,
JR.
in phenol, o- or m-cresol enhanced activity a significant tenfold, or an average threefold greater display of fungistatic potency by the isomeric p-chloro derivatives. The increased increment of fungistatic activity is about the same, and in some instances greater, for other isomeric alkylchlorophenols. The relative germicidal activity for several
Fra. 1. Inhibitory effect of o-chlorophenol and related derivatives on A. niger growth as observed after the 96-hr. incubation period. Concentrations of each derivative were consistently the same as those for o-chlorophenol (compound l), aa follows: 1, 10.0X; 2, 7.5X; 3, 5.0X; 4, 2.5X; and 5, 1.0 X lo-* M.
isomeric alkylchlorophenols ascertained by an analysis of the phenol coefficient data of Klarmann et al. (73) indicates that o-alkyl-pchlorophenols are generally twofold more effective than the o-chlorop-alkyl isomers. Mason et al. (12), in their fungistatic analyses, also using A. niger as the test organism, found that p-chlorophenol is twice as effective as the isomeric o-chlorophenol.
CHEMICAL
STRUCTURE
ON
FUNGAL
ACTIVITY.
III
421
The effect on fungistatic potency caused by introducing various alkyl groups into the o-chlorophenol molecule can be graphically seen from the dosage-response data in Fig. 1. Results for compounds 1 to 7, inclusive, clearly show the enhanced activity resulting from substituting varying weights of alkyls in the para-position. It is interesting to compare the respective activities of compounds 8 and 9 as well as those of compounds lo-16 inclusive, and to note that wherever substitution occurs in the 6-position of o-chlorophenol, fungistatic potency is of a relatively low order, and, in fact, sometimes decreased to a level lower than that for o-chlorophenol itself. Comparison of activities of the isomers represented by compounds 2 and 11, and 4 and 13, further demonstrates the effect on fungitoxicity resulting from steric hindrance of the phenolic hydroxyl group. Isomeric o-chloroxylenols (compounds 17 and IS), in which the methyl groupings are so positioned that steric hindrance of the hydroxyl group is absent, possess a fair degree of fungistatic efficacy, comparable to the activity of other derivatives (compounds 3-6 inclusive), which are devoid of such interference. While the o-chloroxylenols display a moderate amount of fungistatic potency, it is noteworthy to observe that essentially the same activity is found in p-ethyl-o-chlorophenol (compound 3), where the same number of carbons is contained within one alkyl radical. An additional effect attributable to the degree of alkylation within the molecule is noted by comparison of the activities of compounds 2 and 17, in which the molecular difference is one of an additional methyl group in compound 17. Since the limited fungitoxicity data for isomeric phenyl- and cyclohexyl-o-chlorophenols, as included in Table I, do not permit adequate evaluation, additional inhibitory values determined at lower dosage levels are presented in Figs. 2 and 3 together with the response incurred by parallel concentrations of the proven fungicide G-4, 2,2’-methylenebis(4-chlorophenol) . Once again the p-substituted o-chlorophenols, particularly at concentrations of 10U3 to 1O-4 M, are significantly more fungistatic than their respective isomers when the substituent is located in the 6-position. While these data demonstrate that p-phenyl- and p-cyclohexyl-ochlorophenol produce approximately the same crippling effects on the mass growth of A. niger as that caused by similar concentrations of G-4, these chlorinated derivatives, like many of the other sterically unhindered derivatives, possess the additional trait of interfering with the
422
HAROLD
G. SHIRK
AND
ROLAND
R. COREY,
JR.
spore-forming mechanism of the fungus. In fact, at dosage levels which inflicted 60% or more inhibition of mycelial growth, sporulation was either greatly reduced or completely absent. On the other hand, G-4
1.0
10.0
MOLAR
100
FIG. 2. The influence of isomeric phenyl-o-chlorophenols
1.0
0.1 MOLAR
Fro. 3. Relative
inhibitory
XIO’S
CONCENTRATION
IO.0
on the growth of A. dyer.
100.0
x10-s
CONCENTRATION
effect of isomeric cyclohexyl-o-chlorophenols
on
A. niger growth including the dosage-response effect of 2,2’-methylenebis(4chloro-
phenol) (G-4).
dosage levels, which produced comparable growth inhibitory effects, seemingly stimulated the spore-forming capability of A. niger. ACKNOWLEDGMENTS
The authors are indebted to Gilbert Thiessen of Koppers Co., Inc.; F. B. Smith of Dow Chemical Co.; W. S. Gump of Givaudan-Delawanna, Inc.; and M. Macpherson of Sharples Chemicals, Inc. for supplying samples of the compounds used in this investigation.
CHEMICAL STRUCTURE
ON
FUNGAL ACTIVITY.
III
423
SUMMARY
The assay of 17 o-chlorophenols for fungistatic potency has indicated that these derivatives are not, in general, significantly more effective in inhibiting the growth of Aspergillus niger than are the parent phenols devoid of the o-chloro group. Only in phenol and p-cresol did the ortho-introduction of chlorine result in derivatives possessing more marked fungistatic activity. In the case of phenol, there was a threefold increase; with p-cresol, a twofold increase. Fungistatic activity was at a low level in those o-chlorophenols which contain alkyl constituents in the remaining ortho-position. Only p-cyclohexyl- and p-phenyl-o-chlorophenol exhibited fungistatic properties comparable with the proven fungicide, G-4, and, in contrast to G-4, exerted a crippling action on the spore-forming mechanism of A. niger. REFERENCES 1. COOPER, E. A., AND WOODHOUSE, D. L., Biochem. J. 17, 600 (1923). 2. GERSDORFF, W. A., AND SMITH, L. E., Am. J. Pharm. 112, 197 (1940). 3. GRUENHAQEN, R. H., WOLF, P. A., AND DUNN, E. E., Contribs. Boyce Thompson Inst. 16, 349 (1951). 4. HATFIELD, I., Proc. Am. Woo&Preservers’ Assoc. 31 st Ann. Meeting, 57 (1935). 5. KURODA, T., Arch. esptl. Path. Pharmakol. 112, 60 (1926). 6. WOODWARD, G. J., KINOERY, L. B., AND WILLIAMS, R. J., J. Lab. Clin. Med. 19, 1216 (1934). 7. KLARMANN, I& SHTERNOV, V. Am.,AND GATES, L. W., J. Lab. Clin. Med. 20,40 (1934). 8. KLARMANN, E., SHTERNOV, V. A., AND GATES, L. W., J. Am. Chem. Sot. 66, 2576 (1933). 9. BLICKE, F. F., AND STOCKHAUS, R. P. G., J. Am. Pharm. Assoc., Sci. Ed. 22, 1090 (1933). 10. SHIRK, H. G., POELMA, P. L., AND COREY, R. R., JR., Arch. Biochem. Biophys. 32, 386 (1951). 11. SHIRK, H. G., COREY, R. R., JR., AND POELMA, P. L., Arch. Biochem. Biophys. 32, 392 (1951). 12. MASON, C. T., BROWN, R. W., AND MINGA, A. E., Phytopathology 41,164 (1951).
From the Prevention Washington,
Received February 11, 1952 INTRODUCTION
The various isomeric forms of monochlorophenol, including its mono- and polyalkyl derivatives, have very often been included in the search for more efficient fungicides. Cooper and Woodhouse (I), Gersdorff and Smith (2), Gruenhagen, Wolf, and Dunn (3), Hatfield (4), Kuroda (5), and Woodward, Kingery, and Williams (6) have concluded that the paru-positioning of chlorine in phenol or its alkyl derivatives, in contrast to o&ho-positioning, produces more efficacious chemicals as regards their fungicidal activity. A similar generalization appears in the conclusions of Klarmann and his associates (7,8) who examined and compared the relationship between chemical constitution of aliphatic- and aromatic-substituted p- and o-chlorophenols and their germicidal potency. Despite this evidence it appeared desirable, for comparative purposes, to include the o-chlorophenol group of derivatives in the projected search for fungistatic agents. Two earlier papers in this series (10,ll) reported the relative inhibitory effectiveness of p-chlorophenols and the increased fungistatic potency imparted to phenols by para-chlorination. The present work, however, includes both a fungistatic assay of o-chlorophenols and a record of the effect produced by o&ho-chlorination of some alkylated 1 Reported in part before the Conference on Microbiological Deterioration at the Gordon Research Conferences, Am. Assoc. Advancement Sci., July-August, 1950, and sponsored by the Departments of Air Force, Army, and Navy under Contract N7onr-29127. *Present address: College of Agriculture, University of California, Davis, California. 417
418
HAROLD G. SHIRK AND ROLAND R. COREY, JR.
phenols. The results for some derivatives not previously referred to in the literature are included. Except for the systematic studies performed with a homologous series of o-chlorophenols by Klarmann et al. (7,8) and by Blicke and Stockhaus (9), alkyl derivatives of o-chlorophenol have not attracted too much attention as potential antimicrobial agents. METHOD The bioassay procedure employed for evaluating the fungistatic activity of the unhalogenated phenols and numerous o-chlorophenols included in this report was the same as described in the original report of this series by Shirk, Poelma, and Corey (10). RESULTS AND DISCUSSION
The dosage-response data in Table I depict the relative fungistatic efficiency for 17 phenols together with the potency registered for the companion o-chloro compounds. To facilitate evaluation of the effect induced by ortho-chlorination, the interpolated concentration values for each test agent which inflicted a 50% growth inhibitory response are given. In several cases when the lowest concentration (as shown in Table I), caused an inhibition greater than SO%, additional data, not shown here, were used to produce a valid interpolated concentration value. With the exception of phenol, p-cresol, and possibly 3,5-xylenol, the effect induced by ortho-chlorination added nothing to the fungistatic worth of the test compounds; in fact, with many alkylated derivatives chlorine introduction in the ortho-position detracted markedly from the effectiveness of the molecule in inhibiting Aspergillus niger growth. Phenols such as o-isopropyl-, o-phenyl-, o-cyclohexyland the dialkylated derivatives having one of its alkyls in the 6-position, while quite fungistatic in their unhalogenated state, suffered particular dimunition in activity by the introduction of chlorine into the remaining ortho-position. Even the ortho-introduction of chlorine in phenol derivatives devoid of substituents in the second ortho-position, as illustrated by the p-isopropyl-, p-tert-butyl-, p-nonyl-, and p-phenylphenol derivatives, produced compounds which possessed no greater activity than the unhalogenated phenols. Although the fungitoxic properties of p-cresol and phenol were increased an approximate two- to threefold by o&ho-chlorination (as determined by comparing concentrations inhibiting growth 50 %, see Table I), Shirk et al. (11) showed that para-substitution of the halogen
CHEMICAL
STRUCTURE
ON
TABLE Effect
--
of Some Substituted
Compound
Phenol o-Chlorophenol p-Cresol o-Chloro-p-cresol o-Cresol 6-Chloro-o-cresol p-Isopropylphenol o-Chloro-p-isopropylphenol o-Isopropylphenol 6-Chloro-o-isopropylphenol p-tert-Butylphenol o-Chloro-p-tert-butylphenol p-Nonylphenol o-Chloro-p-nonylphenol p-Phenylphenol o-Chloro-p-phenylphenol” o-Phenylphenol 6-Chloro-o-phenylphenol o-Cyclohexylphenol 6-Chloro-o-cyclohexylphenol 3,5-Xylenol o-Chloro-3,5-xylenol p-tert-Butyl-o-cresol 6-Chloro-p-fert-butyl-o-cresol 6-tert-Butyl-m-cresol o-Chloro-6-tert-butyl-m-cresol o-tert-Butyl-p-cresol 6-Chloro-o-tert-butyl-p-cresol 2,4-Diisopropylphenol 6-Chloro-2,4-diisopropylphenol 4,6-DCtert-butyl-m-cresol o-Chloro-4,6-di-tert-butyl-mcresol 2,CDiamylphenolb 6-Chloro-2,4-diamylphenolb
Phenols
FUNGAL
ACTIVITY.
I
and Their o-Chloro of A. niger
Derivatives
Percent inhibition of growth Concentration (10-a M) 5.0 2.5 1.0 10.0 7.5
7---40 33 36 29 58 47 33 25 38 32 100 82 Tr.” 82 79 69 24 19 Tr. Tr. Tr. 92 100 100 67 65 100 100 100 100 100 100 Tr. Tr. 100 100 Tr. 92 68 61 84 82 100 91 46 35 100 98 45 28 100 100 47 27 100 92 62 54 77 75 24 69 13
15 68 9
419
III
25 23 35 18 23 56 63 51 17 76 77 Tr. 63 Tr. 100 Tr. 92 100 87 46 61 69 18 81 15 82 18 76 47 69
10 15 23 12 9 32 32 29 12 40 46 Tr. 57 80 82 87 68 81 65 30 24 40 12 55 7 66 5 54 29 68
4 7 13 7 3 23 16 16 4 25 29 69 46 51 50 68 51 51 43 13 22 24 3 39 6 37 0 37 14 63
9 6 4 64 64 54 12 9 9
on the Growth
e;;g growth x lo-’
50% iki
45 14 18 8.5 18 17 4.5 4.0 5 25 3.5 3.0 0.75 1.50 1.0 1.0 0.8 1.0 1.0 1.4 5.5 4.5 3.5 10.5 2.3 12 1.5 12 2.2 6 >50 0.9 >lOO
Effect of o-chlorination on fungitoxicity
f + 0 0 Neg. 0 Neg. 0 Neg. Neg. + Neg. Neg. Neg. Neg.
Neg. Neg.
mDowicide 4, 85% o-Chloro-p-phenylphenol. b Mixture of secondary and tertiary amyl substituents. c Tr. = trace of mycelial development and growth noted but could not be measured accurately.
420
HAROLD
G. SHIRK
AND
ROLAND
R.
COREY,
JR.
in phenol, o- or m-cresol enhanced activity a significant tenfold, or an average threefold greater display of fungistatic potency by the isomeric p-chloro derivatives. The increased increment of fungistatic activity is about the same, and in some instances greater, for other isomeric alkylchlorophenols. The relative germicidal activity for several
Fra. 1. Inhibitory effect of o-chlorophenol and related derivatives on A. niger growth as observed after the 96-hr. incubation period. Concentrations of each derivative were consistently the same as those for o-chlorophenol (compound l), aa follows: 1, 10.0X; 2, 7.5X; 3, 5.0X; 4, 2.5X; and 5, 1.0 X lo-* M.
isomeric alkylchlorophenols ascertained by an analysis of the phenol coefficient data of Klarmann et al. (73) indicates that o-alkyl-pchlorophenols are generally twofold more effective than the o-chlorop-alkyl isomers. Mason et al. (12), in their fungistatic analyses, also using A. niger as the test organism, found that p-chlorophenol is twice as effective as the isomeric o-chlorophenol.
CHEMICAL
STRUCTURE
ON
FUNGAL
ACTIVITY.
III
421
The effect on fungistatic potency caused by introducing various alkyl groups into the o-chlorophenol molecule can be graphically seen from the dosage-response data in Fig. 1. Results for compounds 1 to 7, inclusive, clearly show the enhanced activity resulting from substituting varying weights of alkyls in the para-position. It is interesting to compare the respective activities of compounds 8 and 9 as well as those of compounds lo-16 inclusive, and to note that wherever substitution occurs in the 6-position of o-chlorophenol, fungistatic potency is of a relatively low order, and, in fact, sometimes decreased to a level lower than that for o-chlorophenol itself. Comparison of activities of the isomers represented by compounds 2 and 11, and 4 and 13, further demonstrates the effect on fungitoxicity resulting from steric hindrance of the phenolic hydroxyl group. Isomeric o-chloroxylenols (compounds 17 and IS), in which the methyl groupings are so positioned that steric hindrance of the hydroxyl group is absent, possess a fair degree of fungistatic efficacy, comparable to the activity of other derivatives (compounds 3-6 inclusive), which are devoid of such interference. While the o-chloroxylenols display a moderate amount of fungistatic potency, it is noteworthy to observe that essentially the same activity is found in p-ethyl-o-chlorophenol (compound 3), where the same number of carbons is contained within one alkyl radical. An additional effect attributable to the degree of alkylation within the molecule is noted by comparison of the activities of compounds 2 and 17, in which the molecular difference is one of an additional methyl group in compound 17. Since the limited fungitoxicity data for isomeric phenyl- and cyclohexyl-o-chlorophenols, as included in Table I, do not permit adequate evaluation, additional inhibitory values determined at lower dosage levels are presented in Figs. 2 and 3 together with the response incurred by parallel concentrations of the proven fungicide G-4, 2,2’-methylenebis(4-chlorophenol) . Once again the p-substituted o-chlorophenols, particularly at concentrations of 10U3 to 1O-4 M, are significantly more fungistatic than their respective isomers when the substituent is located in the 6-position. While these data demonstrate that p-phenyl- and p-cyclohexyl-ochlorophenol produce approximately the same crippling effects on the mass growth of A. niger as that caused by similar concentrations of G-4, these chlorinated derivatives, like many of the other sterically unhindered derivatives, possess the additional trait of interfering with the
422
HAROLD
G. SHIRK
AND
ROLAND
R. COREY,
JR.
spore-forming mechanism of the fungus. In fact, at dosage levels which inflicted 60% or more inhibition of mycelial growth, sporulation was either greatly reduced or completely absent. On the other hand, G-4
1.0
10.0
MOLAR
100
FIG. 2. The influence of isomeric phenyl-o-chlorophenols
1.0
0.1 MOLAR
Fro. 3. Relative
inhibitory
XIO’S
CONCENTRATION
IO.0
on the growth of A. dyer.
100.0
x10-s
CONCENTRATION
effect of isomeric cyclohexyl-o-chlorophenols
on
A. niger growth including the dosage-response effect of 2,2’-methylenebis(4chloro-
phenol) (G-4).
dosage levels, which produced comparable growth inhibitory effects, seemingly stimulated the spore-forming capability of A. niger. ACKNOWLEDGMENTS
The authors are indebted to Gilbert Thiessen of Koppers Co., Inc.; F. B. Smith of Dow Chemical Co.; W. S. Gump of Givaudan-Delawanna, Inc.; and M. Macpherson of Sharples Chemicals, Inc. for supplying samples of the compounds used in this investigation.
CHEMICAL STRUCTURE
ON
FUNGAL ACTIVITY.
III
423
SUMMARY
The assay of 17 o-chlorophenols for fungistatic potency has indicated that these derivatives are not, in general, significantly more effective in inhibiting the growth of Aspergillus niger than are the parent phenols devoid of the o-chloro group. Only in phenol and p-cresol did the ortho-introduction of chlorine result in derivatives possessing more marked fungistatic activity. In the case of phenol, there was a threefold increase; with p-cresol, a twofold increase. Fungistatic activity was at a low level in those o-chlorophenols which contain alkyl constituents in the remaining ortho-position. Only p-cyclohexyl- and p-phenyl-o-chlorophenol exhibited fungistatic properties comparable with the proven fungicide, G-4, and, in contrast to G-4, exerted a crippling action on the spore-forming mechanism of A. niger. REFERENCES 1. COOPER, E. A., AND WOODHOUSE, D. L., Biochem. J. 17, 600 (1923). 2. GERSDORFF, W. A., AND SMITH, L. E., Am. J. Pharm. 112, 197 (1940). 3. GRUENHAQEN, R. H., WOLF, P. A., AND DUNN, E. E., Contribs. Boyce Thompson Inst. 16, 349 (1951). 4. HATFIELD, I., Proc. Am. Woo&Preservers’ Assoc. 31 st Ann. Meeting, 57 (1935). 5. KURODA, T., Arch. esptl. Path. Pharmakol. 112, 60 (1926). 6. WOODWARD, G. J., KINOERY, L. B., AND WILLIAMS, R. J., J. Lab. Clin. Med. 19, 1216 (1934). 7. KLARMANN, I& SHTERNOV, V. Am.,AND GATES, L. W., J. Lab. Clin. Med. 20,40 (1934). 8. KLARMANN, E., SHTERNOV, V. A., AND GATES, L. W., J. Am. Chem. Sot. 66, 2576 (1933). 9. BLICKE, F. F., AND STOCKHAUS, R. P. G., J. Am. Pharm. Assoc., Sci. Ed. 22, 1090 (1933). 10. SHIRK, H. G., POELMA, P. L., AND COREY, R. R., JR., Arch. Biochem. Biophys. 32, 386 (1951). 11. SHIRK, H. G., COREY, R. R., JR., AND POELMA, P. L., Arch. Biochem. Biophys. 32, 392 (1951). 12. MASON, C. T., BROWN, R. W., AND MINGA, A. E., Phytopathology 41,164 (1951).