Facts (with Timeline):

i) FMC Corporation and FMC Agro Singapore Pte. Ltd. (collectively referred to as “Plaintiffs”) were assigned Indian Patent No. 298645 (suit patent/IN’645) titled “Method for preparing N-Phenylpyrazole-1-Carboxamides.”

ii) The suit patent disclosed a novel method for preparing anthranilic diamide insecticide compounds. The claimed method involves combining:

  • a carboxylic acid compound of Formula 2,
  • an aniline compound of Formula 3, and
  • a sulfonyl chloride,
  • to prepare a compound of Formula 1 (Chlorantraniliprole (CTPR)).

iii) The Plaintiffs brought a suit against Natco Pharma Limited (Defendant) alleging that Defendant’s process to manufacture CTPR infringed on the Plaintiffs’ patented method. The Defendant’s process utilized a carboxylic acid of Formula 2, an aniline compound of Formula 3, and thionyl chloride. Plaintiff claimed that Defendant’s usage of thionyl chloride instead of sulfonyl chloride constituted infringement under the “Doctrine of Equivalents.”

iv) On 23rd May, 2022, on the issuance of a summons, the Defendant stated that they would launch their CTPR product on expiry of two previous product patents (IN 201307 (IN’307) and IN 21332 (IN’332)) pertaining to CTPR —which would expire on 13th August, 2022—and that their method for making CTPR did not infringe on Plaintiffs’ patent IN’645.

v) On 29th July, 2022, with the consent of the parties, two Scientific Advisors were appointed to examine the Plaintiffs’ patented process and the process the Defendant planned to use to manufacture CTPR.


Issue#1 – Does Defendant’s process for manufacturing CTPR infringe the Plaintiffs’ patented process for manufacturing CTPR under the “Doctrine of Equivalents”?


i) According to the “Doctrine of Equivalents,” in the absence of literal infringement, a product/process is found to infringe a patented product/process, if it is found to be its substantial equivalent. An infringing product/process may be a substantial equivalent of a patented product/process if a substituted element in the infringing product/process does the same task,
in substantially the same way, to accomplish substantially the same result.

ii) There is no infringement if an essential element is different (not a substitute) or omitted. There may be an infringement if non-essential elements are substituted or omitted.


Issue#1 – No. To determine if the Defendant’s process was the substantial equivalent of the Plaintiffs’ process, the court looked at the following:

i) the sequence in which the Plaintiffs’ process and the Defendant’s process occurred;

ii) if sulfonyl chloride was an essential element; and

iii) if yes to ‘ii)’, then is thionyl chloride an equivalent of sulfonyl chloride.

i) While claim 1 of the Plaintiffs’ process was not limited to a sequence in which the reactants (carboxylic acid, aniline compound, and sulfonyl chloride) are combined, the court looked at the written description of IN’645 which stated that a preferable sequence for making CTPR took place in a single reactor and involved (1) first mixing the carboxylic acid with the aniline compound (e.g., 2-Amino-5-chloro-N,3- dimethylbenzaraide) to obtain a mixture, and (2) then combining the mixture with a sulfonyl chloride. Despite the written description stating that there may be many orders or sequences in which the reactants could be combined, the court interpreted the sequence of claim 1 as that being of the preferred embodiment.

The Defendant’s process for making CTPR took place in two reactors and involved (1) mixing the carboxylic acid with thionyl chloride in the first reactor to obtain the acid chloride, and (2) then reacting the acid chloride with 2-Amino-5-chloro-N,3- dimethylbenzaraide (the aniline compound) in a second reactor to obtain CTPR.

Based on the above, the court noted that there were differences between the sequences of Plaintiffs’ process and the Defendant’s process.

ii) Both the scientific advisors found that in IN’645, sulfonyl chloride was an essential element for preparing CTPR, and based on the written description of IN’645, the court also reached the same conclusion that sulfonyl chloride was an essential element.

iii) Both the scientific advisors found that thionyl chloride was different from sulfonyl chloride, i.e. thionyl chloride was not an equivalent of sulfonyl chloride, for the following reasons:

a) thionyl chloride (inorganic chloride) had different physical and chemical properties than sulfonyl chloride (organic chloride);

b) in the Defendant’s process, the thionyl chloride acted as a chlorinating agent, and in the Plaintiffs’ process, the sulfonyl chloride acted as a coupling agent; and

c) in the Defendant’s process, the use of thionyl chloride resulted in SO2 (gas) and HCl (gas), which are scrubbed and absorbed in caustic soda solution to give sodium chloride and sodium bisulfite having use in the food and cosmetic industry. In the Plaintiffs’ process, the use of sulfonyl chloride (methane sulfonyl chloride) resulted in the formation of a solid toxic by-product (methane sulfonic acid) which is hazardous to the environment.

Accordingly, the court found that Defendant’s process did not infringe on Plaintiffs’ process.


Natco Pharma’s process for manufacturing CTPR did not infringe FMC Corporation’s patented process for manufacturing CTPR under the “Doctrine of Equivalents” as the sequence of the processes was different, and the use of thionyl chloride was different from sulfonyl chloride (essential element). Thionyl chloride had i) different physical and chemical properties; ii) the usage of thionyl chloride differed from that of sulfonyl chloride, and iii) the result produced by using thionyl chloride had some differences from the result produced by using sulfonyl chloride.

A practical takeaway from this case would be to refrain from explicitly referring to an embodiment as being a preferred one because the court can restrict the scope of a claim to that of the preferred embodiment. In this case, even though claim 1 of IN’645 only mentioned combining three reactants, wherein claim 1 did not limit itself to a specific order or sequence in which the reactants would be combined, the court interpreted claim 1 to be limited to the combining the reactants in the sequence outlined in the preferred embodiment. This limited interpretation had helped Natco Pharma in showing that one of the aspects in which their process differed from FMC Corp’s process was based on the sequence in which the process for manufacturing CTPR took place.

Relevant paragraphs:

Paragraph 15 – “… Claim construction has to be done as a whole and there is also no quarrel that all essential elements of the suit patents claimed are required to be found in the infringing process to establish infringement.”

Paragraph 17 – “… Use of a different reagent and a completely different sequence of reactions in the Natco process cannot be termed as a minor or insubstantial variation, so as to accuse the Defendant of infringement and piracy.”

Paragraph 19 (quoting Free World Trust v Électro Santé Inc, [2000] 2 S.C.R. 1024, 2000 SCC 66) – “… The identification of elements as essential or non-essential is made:
(i) on the basis of the common knowledge of the worker skilled in the art to which the
patent relates;
(ii) as of the date the patent is published;
(iii) having regard to whether or not it was obvious to the skilled reader at the time the patent was published that a variant of a particular element would not make a difference to the way in which the invention works; or
(iv) according to the intent of the inventor, expressed or inferred from the claims, that a particular element is essential irrespective of its practical effect;
(v) without, however, resort to extrinsic evidence of the inventor’s intention.”

Paragraph 25 (quoting scientific advisor Dr. Nair’s report) – “The essential features of the process covered in the suit patent IN’645 comprises combining the carboxylic compound of Formula 2 with the aniline compound of Formula 3 in the base to form a mixture and then addition of the sulfonyl chloride R8S(O)2Cl of Formula 4 to the mixture in a single reactor.”

Paragraph 26 – “In view of the said findings coupled with the specification of IN’645 and the detailed description therein, in my prima facie view, sulfonyl chloride, more particularly, methanesulfonyl chloride is an essential and integral part of the suit patent and on this count, the stand of the Defendant is correct.”

Paragraph 28 – “From the above findings, the prima facie conclusions are (1) sulfonyl chloride is an essential element of the suit patent and (2) thionyl chloride used as a reagent in the Natco process, differs from sulfonyl chloride in its physical and chemical properties. Additionally, it requires mention that in the Natco process, thionyl chloride is used as a chlorinating agent to react with carboxylic acid to displace the -OH group present in the acid and replace it with the chlorine atom to form an acid chloride, while in the Plaintiffs’ process sulfonyl chloride is added to the mixture of a Carboxylic acid, Amide, Analine and a Base to activate the process and thus acts as a ‘coupling agent’ to control the rate of reaction as well as the yield produced by it. In fact, in the case of the Plaintiffs that the advantages of sulfonyl chloride according to IN’645 reside in its utility for acid-amide coupling besides its convenience to use, low cost and the advantage of being able to control the rate of coupling. ‘Chlorination’ is a process in which chlorine is introduced into a molecule while ‘coupling reaction’ refers to a class of organic reactions that involve the joining of two chemical species, usually with the help of a metal catalyst. A coupling agent is a compound which provides a chemical bond between two dissimilar materials, usually inorganic and organic. These chemicals usually modify the surface functionality of filler effectively to aid easy bonding with polymer chains.”

Paragraph 29 (quoting Dr. Nair’s report) – “… Defendant’s Process is distinct from the process claimed in claims 1 to 5 of IN’645. Moreover, in IN’645 sulfonyl chloride is used and also all three reagents i.e. the acid, the aniline compound and sulfonyl chloride are added in a single reactor. In Defendant’s process, the carboxylic acid is first converted to its acid chloride using
thionyl chloride in a first reactor. The acid chloride so obtained is reacted with 2-Amino-5-chloro-N,3- dimethylbenzaraide in another reactor to obtain the final product..”

Paragraph 30 (quoting Dr. Nair’s report) – “… [I]n IN’645 process due to the use of methane sulfonyl chloride there is the formation of the solid toxic by-product methane sulfonic acid which is hazardous to the environment. In Defendant’s process, the use of thionyl chloride results in the liberation of SO2 (gas) and HCl (gas). The liberated gases are scrubbed and absorbed in caustic soda solution to give sodium chloride and sodium bisulfite having been used in the food and cosmetic industry.

The results of the reaction using methane sulfonyl chloride in the suit patent IN’645 compared to the reaction using thionyl chloride in the defendant’s process do not produce the same result in view of the resultant characteristics of the by-products and impact of the impurity profile of the final product.

As such, there is no literal equivalence between the Defendant’s process and Plaintiffs’ IN’645 process.”

Paragraph 36 – “The Advisors were appointed with the consent and agreement of the parties and needless to state their opinion and findings need to be respected. Moreover, there is no challenge to the findings of the Advisors. Learned counsel for the Defendant has rightly relied on the judgment of the Supreme Court in Martin F. D’Souza (supra), for the proposition that Courts are not experts and should not substitute their views or opinion for those of the experts or specialists in the field.”

Citation: FMC Corporation & Ors. vs. Natco Pharma Limited on 19 September, 2022 (CS(COMM) 349/2022 & I.A. 8132/2022, 9519/2022, 10886/2022) available at: https://indiankanoon.org/doc/51656490/

This post is brought to you by Mr. Nikhil Radhakrishnan, Patent Associate.

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