Working Paper

Leveraging Cheminformatics to Bolster the Control of Chemical Warfare Agents and their Precursors

Examining the capability of a cheminformatics tool to help help keep track of chemicals and close the proliferation loophole
By Richard Cupitt Co-author

This article was also co-authored by Stefano Costanzi and Gregory D. Klobentz.1Stefano Costanzi is an Associate Professor of Chemistry at American University with an educational background in both the chemical sciences and international affairs. His current scholarly work is based on two research lines: the computational modeling of the interactions between chemicals and living organisms; the analysis of gaps in current policies and practices that allow the proliferation of chemical weapons and the conceptualization of solutions and tools to narrow them. Gregory D. Koblentz is an Associate Professor and Director of the Biodefense Graduate Program at George Mason University’s Schar School of Policy and Government. He is also an Associate Faculty at the Center for Security Policy Studies at George Mason and a member of the Scientist Working Group on Biological and Chemical Security at the Center for Arms Control and Nonproliferation.


International frameworks and national legislation contain lists of controlled chemicals that can be employed as chemical warfare agents or precursors for their synthesis. The development and wide adoption of a cheminformatics tool could overcome several practical problems inherent to the way in which the identification of such chemicals is currently conducted, namely: the same chemical can be identified with a multitude of synonyms; different versions of the same chemical, for instance isotopically labeled versions, have different registry numbers; some lists define whole families of related chemicals of concern in a single entry, thus complicating certification of compliance; and lists of controlled chemicals are subject to change and must be kept current. Composed of an up-to-date database of relevant lists of controlled chemicals with an associated easy-to-use software, this tool would help address these problems by converting any entered chemical name or registry number into a chemical structure, and automatically checking whether that structure matches any entry of the database. Efforts by the Pistoia Alliance for the control of regulated narcotic and psychotropic substances has led to the development of commercial software that can be used as a starting point for the development of the proposed cheminformatics tool for nonproliferation purposes. By helping frontline officers and chemical industry to handle families of chemicals, this cheminformatics tool could facilitate the inclusion of families of chemicals in control lists, thus closing potential proliferation loopholes. Finally, beyond chemical warfare agents and precursors, this cheminformatics tool could be generally used to handle any list of controlled chemicals.

Introduction: International Lists for the Control of Chemical Warfare Agents
and Precursors

A number of international frameworks such as the nearly universal Chemical Weapons Convention (CWC), the Australia Group (AG), and the Wassenaar Arrangement, contribute to a coordinated multilateral effort to stem the proliferation of chemical weapons (CW). To serve this purpose, these frameworks contain lists of chemicals that can be employed as chemical warfare agents (i.e. the toxic chemicals on which chemical weapons are based) or precursors for their synthesis. Some of the lists exclusively comprise individual chemicals, with each entry in the list identifying a specific chemical. Other lists comprise both individual chemicals as well as families of related chemicals, defined as a central chemical scaffold bearing a number of attached variable chemical groups. Both types of entries consist of one chemical name, with no synonyms given, which identifies either an individual chemical or a family of chemicals. Moreover, for individual chemicals, the lists also report the associated Chemical Abstract Service (CAS) registry number.2The Chemical Abstract Service (CAS, Registry of the American Chemical Society is a collection of the disclosed information available on chemical substances published in the scientific literature. Each substance in the registry is assigned a unique numeric identifier, the CAS Registry Number. In the paragraphs below, the authors give a brief survey of the lists contained in the above-mentioned international frameworks. Subsequently, the remainder of the article is dedicated to discussion regarding why dealing with lists composed of chemical names and registry numbers makes it impractical to identify controlled chemicals and discuss how such problems could be overcome by the development and wide adoption of a suitable cheminformatics tool.

In its Annex on Chemicals, the CWC contains a tiered system of three schedules of chemicals
meant to support the verification regime imposed by the convention.3The 1993 CWC is an international treaty that poses a complete ban on chemical weapons and has currently been ratified or acceded to by 193 State Parties; Organisation for the Prohibition of Chemical Weapons (OPCW), Chemical Weapons Convention, Importantly, beyond supporting the Convention’s declaration requirements and verification regime, the CWC schedules are also incorporated by various countries in their export control lists. Each schedule is divided into a part A, which lists chemical warfare agents, and a part B, which lists chemical precursors. Schedule 1 comprises chemicals that are regarded exclusively or almost exclusively as chemical warfare agents or precursors for their synthesis. Conversely, Schedules 2 and 3 comprise dual-use chemicals that also have legitimate, non-military commercial applications, on a smaller scale for Schedule 2, and on a larger scale for Schedule 3.4CWC Annex on Chemicals, While some of the entries in the CWC schedules identify individual chemicals, others identify families of related chemicals. Including families of chemicals in the CWC schedules is important as it allows a single entry to cover a large group of structurally related chemicals without the need to enumerate them.5Stefano Costanzi and Gregory D. Koblentz, “Controlling Novichoks After Salisbury: Revising the Chemical Weapons Convention Schedules,” The Nonproliferation Review (2019), To avoid confusion, it should be noted that the CWC schedules do not need to be taken as an exhaustive list of chemical warfare agents. Indeed, the CWC does not limit the definition of chemical weapons to those in the schedules, but includes all “toxic chemicals and their precursors, except where intended for purposes not prohibited under this Convention, as long as the types and quantities are consistent with such purposes.”6In CWC Article II, Paragraph 1 (a), https://www.opcw/chemical-weapons-convention/articles/article-ii-definitions-and-criteria.

The Australia Group, a group of more than 40 countries that coordinate their export control regulations on dual-use equipment and material that could be used to produce chemical and biological weapons, has compiled a list of chemicals that can be used as precursors for the synthesis of chemical warfare agents.7Australia Group, The Australia Group’s “Chemical Weapons Precursors” list comprises a total of 65 chemicals. Of these, 40 are listed in part B of one of the three CWC schedules (either as individual chemicals, or by virtue of being included in one of the families of chemicals listed in the CWC schedules). Conversely, the remaining 25 chemicals are not covered by the CWC schedules. The Australia Group’s Chemical Weapons Precursors list, however, does not include families of chemicals. Instead, the 65 chemicals that it covers are explicitly enumerated as individual compounds.

Similarly, the Wassenaar Arrangement, an international framework that was established in 1996 to provide greater transparency of transfers of conventional weapons and dual-use items, includes on its Munitions List 7 (ML7), inter alia, a range of chemical agents with military applications.8The Wassenaar Arrangement, In particular, the chemical agents listed in ML7 include the CWC Schedule 1 chemicals, the incapacitating agent 3-quinuclidinyl benzilate (BZ), which is a CWC Schedule 2 chemical, and lists of chemical defoliants and riot control agents, neither of which is included in the CWC schedules. With the exception of the families of chemicals listed in CWC Schedule 1, all the remaining CW-related entries in the Wassenaar Arrangement ML7 are enumerated as individual chemicals. Beyond CW proliferation, two other export control arrangements, the Nuclear Suppliers Group (NSG) and the Missile Technology Control Regime (MTCR), include chemicals that are regarded as a threat for nuclear and missile proliferation in their control lists, explicitly enumerated as single chemicals and annotated with CAS registry numbers.

Other lists of controlled chemicals, often based on the lists in the above-mentioned international frameworks, have been crafted by international and domestic bodies to support the implementation of the CWC mandates, export controls, and homeland security. For example, the World Customs Organization (WCO), through its Strategic Trade Control Enforcement (STCE) Implementation Guide, provides, inter alia, information to customs administrations on how to implement trade controls on strategic chemicals, and contains an annex (Annex V) that compiles many of the individual chemicals (but not families of chemicals) listed by the CWC, Australia Group, NSG, MTCR, and the Wassenaar Arrangement.9World Customs Organization, “Strategic Trade Control Enforcement Implementation Guide,” 2019, Annex V, which lists more than 250 chemicals by CAS number, appears on pages 143-145. As another example, the Chemical Facility Anti-Terrorism Standards (CFATS) of the U.S. Department of Homeland Security (DHS) contains an appendix (Appendix A) that provides a list of more than 300 chemicals of interest, including, inter alia, chemical warfare agents and precursors for their synthesis.10U.S. Department of Homeland Security, “CFATS, Appendix A: Chemicals of Interest (COI),”

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