In re Kilsheimer (349 F.2d 441, 1965)

MARTIN, Judge.

John R. Kilsheimer and Harry L. Haynes appeal the decision of the board, adhered to on reconsideration, affirming the examiner’s rejection of claims 1 and 5, the only claims remaining in their application serial No. 676,368, filed August 5, 1957 for “3-Isopropylphenyl N-Methyl-carbamate and Insecticidal Compositions Containing the Same.”

The invention, a chemical compound which appellants have discovered is an effective insecticide, is claimed as follows:

1. 3-Isopropylphenyl N-methyl-carbamate.

5. The method of killing insects which comprises applying 3-isopro-pylphenyl N-methylcarbamate to said insects.

The compound of the claims, 3-isopropylphenyl N-methylcarbamate, has the following structure:

The 3-position on the phenyl ring is also known as the meta position, that is, a substituent on the 3-position is meta, or m-, to the N-methylcarbamate group. Accordingly, appellants’ compound could be called meta- (or m-)isopropylphenyl N-methylcarbamate. Similarly a substit-uent on the 2-position may be termed an ortho, or 0-, substituent, and one on the 4-position may be termed a para, or p-, substituent. We will be concerned with the several positions of a substituent, primarily the isopropyl group, on the ring.

Two major classes of insecticides, phosphorus- and chlorine-containing insecticides, suffer from a number of disadvantages, primarily cost, mammalian toxicity, and the growing resistance of insects to those classes of insecticides. Because of such disadvantages, research has been conducted to discover and develop other classes of insecticides. The carbamates, of which the present invention is a member, have proven of value.

The dosage of an insecticide which is required to kill 50 per cent of insects, such as houseflies, is known as the LD60.

An increase in the LD5o dosage required against succeeding generations of flies bred from the survivors of a treatment shows a tolerance for, or an accommodation or resistance to the insecticide. As well as finding that the 3-isopropylphenyl' N-methylcarbamate is lethal to “a wide variety of insects, arachnids and other agricultural and household pests, including aphids, mites, army worm larvae, beetles, flys [sic], roaches and mosquitos [sic],” the compound “is a particularly valuable insecticide, since insect strains controlled by it have not developed immunity to it.” Appellants disclose that:

* * * It was found in a series of tests that the LD50 (dosage to kill 50 per cent of the flies tested) for the twentieth generation was approximately the same as the LD50 for the starting generation.

Appellants disclose a series of tests which indicate that the claimed 3-isopropylphe-nyl N-methylcarbamate, abbreviated IPMC, is superior to several typical commercial insecticides, compounds X [1,1,1-trichloro - 2,2 - bis - (p - chlorophenyl) ethane], Y [a chlorinated camphene], and Z [3-tertiary-butylphenyl N-methylcar-bamate (which it will be seen below is one of the reference compounds)]. The application states:

TABLE I

Cone, of chemical in mg./100 ml. of water required to kill 95 per cent (LDg5)

Compound Spider mite adults Southern army worm larvae House fly (poison bait) Aphid

IPMC 78 40 15 17

Compound X >•250 82 28 20

Compound Y >250 14 20 32

It can be seen that in Table I IPMC is, with one exception, superior in every way to commercial compounds X and Y.

IPMC has also been compared with a closely related carbamate, 3-ter-tiarybutylphenyl N-methylcarba-mate (compound Z) by the above tests, as well as by the Roach Immersion Test, the Mosquito Larvae Test and the House Fly Topical Application Test. The results of these tests are reported in Table II. A cholinesterase determination was also made on these two materials and the results reported in Table III. * * *

***•»*•»

TABLE II

Compound

IPMC

Compd. Z

Roach

250

400

Mosquito larvae

1.4

4.6

Spider mite adults

78

130

Southern army worm larvae

40

80

House fly (poison bait)

15

>120***

Aphid

17

80

House fly Topical Application

2

40

*** Note: With an acceptable formulation, it is possible to get 30 mg./100 ml. of HiO in solution. This provides 30 per cent kill. Above 30 mg. and including a 120 mg. dosage, a suspension is obtained These suspensions do not increase kill above 30 per cent.

TABLE III

Compound Cholinesterase Inhibition, I50

IPMC 1.5 x 10-7

Compound Z 2.2 x 10-7

It can be seen from Tables II and III that 3-isopropylphenyl N-methyl-carbamate is an outstanding insecticide, which is superior in every respect to compound Z.

The single reference on which the compound and method of use claims are rejected is:

Kolbezen, et al. INSECTICIDE STRUCTURE AND ACTIVITY.

Insecticidal Activity of Carba-mate Cholinesterase Inhibitors. Agricultural and Food Chemistry, Yol. 2, No. 17, August 18, 1954, pp. 864-70.

Kolbezen et al. disclose the preparation and toxic evaluation of some 30 N-methylcarbamate esters of substituted phenols. The Kolbezen et al. paper opens with a short discussion of the reasoning which led them to their compounds. It stands as an example of the predictive approach of which modern chemistry is capable (footnotes omitted):

Most of the organic insecticides in common use today were discovered during the routine screening of many miscellaneous chemicals or by the planned synthesis of derivatives of compounds already known to be effective. Few if any have been developed from the biochemical viewpoint of devising an antimetabolite or enzyme antagonist that would possess the proper prerequisites for contact toxicity, although the present status of knowledge in this field seems adequate for such an undertaking.

With this general concept in mind, the authors selected the cholinester-ase (ChE) enzyme system of insects as a starting point because of its vital function in the neural behavior of the organism and the considerable information available concerning its properties and functions. * * *

The carbamic acid esters have long been known to be highly effective inhibitors of cholinesterases, and as such they have pharmacological applications. These compounds have structural configurations that closely resemble the choline esters, and their inhibitory activity occurs from the resulting strong attraction to the active center of the enzyme and their much greater stability to hydrolysis. * * * Therefore, this group of compounds was chosen as the starting point of an investigation of the requirements for converting potent enzyme inhibitors into contact insecticides.

Kolbezen et al. continue the background discussion, indicating that their investigation of carbamate esters of phenols was based on the knowledge that:

Insect nerves are known to be surrounded by lipoid sheaths, and it is probable that ready penetration of cholinesterase inhibitors into the nervous system is facilitated by non-polar lipoid-soluble molecules rather than by the highly polar quaternary ammonium compounds. Therefore, attention was turned toward the synthesis of a representative series of N-substituted carbamates of substituted phenols. * * *

The Kolbezen et al. prediction was correct:

Since this investigation was begun, the validity of the assumption that nonpolar lipoid-soluble carba-mate derivatives should be contact toxicants has been amply confirmed by extensive investigations of a large series of N-alkyl carbamates of psuedoaromatic [sic] and cyclic alcohols. Certain of these materials, particularly l-phenyI-3-methylypra-zolyl- (5) -dimethylcarbamate (pyro-lan) and l-isopropyl-3-methylpyra-zolyl- (5) -dimethylcarbamate (iso-Ian), showed outstanding toxicity to aphids, thrips, flies, and other insects, both by contact and per os.

* * *

Kolbezen et al. then disclose their N-methylcarbamates to be prepared from the reaction of methyl isocyanate with the desired substituted phenol. Both cholinesterase inhibition and toxicity tests were run, and the following results are taken from their Table 1:

Table 1. Properties and Biological Activity of N-Methylcarbamates of Various Phenols

Housefly

N-Methylearbamate Iso” LD50 Y/g MLC° thrips

* ***** * * * * * * *

VI o-lsopropylphenyl 6 x 10-6 100 0.00018

VII p-Isopropylphenyl 7 x 10-5 >500 0.023

VIII o-tert-Butylphenyl 6 x 10-8 75 0.00015

IX m-tert-Butylphenyl 4 x 10-7 50 0.00008

X p-tert-Butylphenyl 1.5 x 10~4 >500 >0.1

* ***** * * * * * * *

XXI 2-Methyl-5-isopropylphenyl 2 x 10-8 >500 0.00025

* * * * * * * * * * * * * *

b. Molar concentration for 50% inhibition of fly-brain cholinesterase

c. Median lethal concentration, %

Kolbezen et al. state the following concerning the tests:

Discussion of Results

Relation of Structure to Toxicity

The results presented in Tables I and II indicate the identity of the carbamates synthesized, their toxicity as contact insecticides to the female housefly, Musca, domestica L., and to the greenhouse thrips, Heliothrips haemorrhoidalis (Bouche), and the molar concentration required in vitro for 50% inhibition of fly-brain cholinesterase. The more toxic compounds were also evaluated as contact toxicants to the green citrus aphid, Aphis spiraecola Patch, and to the citrus red mite, Paratetranychus citri (McG.). .They exhibited approximately the same degree of toxicity to the aphid as to the thrips, but the most effective compound (IX) produced only 73% mortality of the citrus red mite adult at 0.1% concentration. * * *

The compound considered by Kolbezen et al. to be the most active compound of those insecticides tested, compound IX, mefa-tert-butylphenyl N-methylcarbamate, is the next higher homolog of appellants’ claimed compound. The tert-butyl substituent is also disclosed at the ortho and para positions.

It is also evident that the Kolbezen et al. compounds VI and VII are respectively the ortho and para position isomers of appellants’ compounds, thus:

Kolbezen et al. VI 2-, or ortho-isopro-pylphenyl N-methyl-carbamate

Kolbezen et al. VII 4-, or para-isopro-pylphenyl N-methyl-carbamate

Appellants’ 3-, or meta-iso-propylphenyl N-methylcarbamate

Kolbezen et al. further discuss the relation of structure to toxicity as follows, noting first the relationship between the type of phenyl ring substituent and the cholinesterase inhibition (I50 in Kolbezen et al. Table I above):

The nature and extent of substitution of the phenyl rings of the N-methylcarbamates exert a remarkable influence on toxicity. The order of effectiveness of single ring substituents upon cholinesterase inhibition was N02 < Cl < CH3 < C2H5 < iso-CsHj < (CH3)2 N < tert-CJI9 < (CH3)3N+I, * * * [Emphasis ours.]

Insofar as we are concerned here, that disclosure of Kolbezen et al. indicates the isopropyl group to be a less effective cholinesterase inhibitor than the tert-butyl group as a substituent on the phenyl ring. With regard to contact toxicity, Kolbezen et al. indicate the order of effectiveness of the various sub-stituents quoted just above to be only “roughly in the same order * * with an exception which does not concern us here.

In discussing the placement of the substituents on the phenyl ring as related to cholinesterase inhibition and toxicity, Kolbezen et al, teach that the meta position is the most effective and para is least:

* * * The order of effectiveness of ring position was p < o