Chemical names are a problem. Not because they are wrong, but because they are inconsistent. The same compound can go by a formal IUPAC name that runs to forty syllables, a common name that varies by country, a brand name assigned by whoever manufactures it, and a handful of informal abbreviations that circulate in research literature. For a scientist trying to confirm that the compound referenced in a 1987 Japanese study is the same one appearing in a 2019 German trial, this proliferation of names is genuinely inconvenient. The CAS number exists to solve that problem. It is a simple, unambiguous identifier that follows a chemical compound wherever it goes, regardless of what anyone decides to call it.
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What CAS Numbers Are and Where They Come From
CAS stands for Chemical Abstracts Service, a division of the American Chemical Society that has been indexing chemical literature since 1907. The CAS Registry, which the organization maintains, is the world’s largest database of chemical substance information, containing records for well over two hundred million unique substances as of recent counts.
The Registry and Its Origins
The CAS Registry began as a response to the growing volume of chemical literature in the early twentieth century. As the number of known compounds expanded rapidly, researchers needed a reliable way to search for and cross-reference chemical information across different publications, languages, and naming conventions. The Registry assigned a unique numerical identifier to each substance it catalogued, creating a system that was language-neutral, naming-convention-neutral, and completely unambiguous. That numerical identifier is what we now call a CAS Registry Number, or CAS number.
The Structure of a CAS Number
A CAS number consists of three groups of digits separated by hyphens, in the format XXXXXXX-YY-Z. The first segment can be up to seven digits long. The second segment is always two digits. The third segment is always a single digit, which functions as a check digit calculated from the other numbers in the sequence using a specific algorithm. This check digit allows software systems to verify that a CAS number has been entered correctly, catching transposition errors before they cause problems. The numbers themselves are assigned sequentially as new substances are registered and carry no chemical meaning. Knowing a compound’s CAS number tells you nothing about its structure, only its identity within the Registry.
Why Researchers Rely on CAS Numbers in Peptide Science
In peptide research specifically, CAS numbers serve several practical functions that make them a standard feature of scientific communication and documentation.
Disambiguation Across Naming Systems
Many research peptides are known by multiple names simultaneously. BPC-157, for example, is also referred to as PL 14736, body protection compound-157, and by its full IUPAC name, which is lengthy enough that almost nobody uses it in conversation. The CAS number for BPC-157, 137525-51-0, is the same regardless of which name appears in the document you are reading. When a researcher sees that number, they know with certainty which compound is being discussed. This disambiguation function is particularly valuable when working across literature from different research groups, countries, or decades.
Database Searching and Cross-Referencing
Major scientific databases including PubChem, ChemSpider, and various proprietary research platforms accept CAS numbers as search inputs. Searching by CAS number rather than by name typically produces cleaner, more reliable results because the search is not subject to spelling variations, abbreviation differences, or translation inconsistencies. A researcher looking for all available data on a specific peptide can use the CAS number to pull records from multiple databases with confidence that each result refers to the same compound.
Quality Assurance and Supplier Documentation
Certificates of analysis issued by research peptide suppliers routinely include the CAS number of the compound alongside its name, purity data, and analytical results. Verifying that the CAS number on a certificate of analysis matches the CAS number of the intended compound is a basic but important quality assurance step. It is a quick cross-check that the product in hand is the product that was ordered, regardless of what name appears on the label.
CAS Numbers in the Context of Peptide Reference Databases
Reference databases that compile peptide information, including publicly available resources like PubChem maintained by the National Institutes of Health, use CAS numbers as one of several cross-reference identifiers for each compound record. A typical PubChem compound page for a research peptide will list the CAS number alongside the compound’s PubChem CID, its IUPAC name, its molecular formula, and any synonyms registered to it. This layered identifier system means that researchers approaching the same compound from different directions, whether through a supplier catalog, a literature search, or a database query, can always converge on the same authoritative record.
It is worth noting that not every chemical compound has a CAS number. Novel compounds that have not yet been registered with the Chemical Abstracts Service, or substances that exist only as theoretical structures, will not have one. For established research peptides that have appeared in the scientific literature, however, a CAS number almost certainly exists and is the most reliable way to anchor communication about that compound.
Frequently Asked Questions About CAS Numbers
CAS numbers come up regularly in peptide research contexts, and a handful of questions about them tend to recur among people who are new to working with chemical reference materials.
- What does a CAS number look like and how is it formatted?
- A CAS number consists of three groups of digits separated by hyphens, for example 137525-51-0. The first group can contain up to seven digits, the second group always contains two digits, and the third group is always a single check digit used to verify the number’s accuracy. The numbers are assigned sequentially and carry no inherent chemical meaning beyond identifying the compound in the registry.
- Can two different compounds share the same CAS number?
- No. Each CAS number is assigned to one and only one chemical substance. The system is designed specifically to prevent ambiguity, so a CAS number is a unique identifier in the same way that a national identification number uniquely identifies a person. Different salts, isomers, or hydrated forms of a compound typically receive their own distinct CAS numbers, since they are considered chemically distinct substances.
- How do I find the CAS number for a specific research peptide?
- The most straightforward way is to search for the peptide by name in PubChem, the free chemical database maintained by the National Institutes of Health. The compound’s PubChem page will list the CAS number under its identifiers section. Supplier certificates of analysis also routinely include CAS numbers, as do most scientific database records for established compounds.
- Is the CAS number the same as the PubChem CID?
- No, these are different identifiers from different systems. The CAS number is assigned by the Chemical Abstracts Service and is used across a wide range of chemical databases and documentation. The PubChem CID is an identifier assigned specifically within the PubChem database maintained by the NIH. Both can be used to look up a compound, and PubChem records typically list the CAS number as one of several cross-reference identifiers, but they are not interchangeable.