Chemistry and Pharmaceuticals Searching Best Practices
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Some technical disciplines require deviations from traditional text and classification search approaches. Chemistry and pharmacology searching is one of the best examples. The problems unique to searching for chemical compounds became apparent as early as the 1960s; to address them, professional indexing companies such as the Chemical Abstracts Service (CAS) and Derwent Ltd. began to produce specially created data files geared towards chemical searchers. This article discusses the special treatment that chemical information receives in the patent world, and the tools and training needed to conduct a thorough search for novel chemical compounds, and pharmacology formulations of known drug compounds.
In addition to the special tools needed to search chemical structures, a chemistry or pharmacology search may require the searcher to consider methods of use, processes for production, and even special physical forms. Therefore, a searcher in this area can sometimes benefit from a background in chemical engineering, biochemistry, biology, and even mechanical engineering.
Note: Although genes are chemical compounds, the techniques discussed below do not fully address the resources and strategies necessary for genetic sequence searching, a type of search usually called for in the biotechnology arts. Please see the biotechnology best practices article for more information on this special type of search.
Obstacles Facing the Searcher
Substance Searching – Names, Numbers and Physical Properties
To the uninitiated, the most obvious way to search for a chemical compound in a patent document is to perform a search on its name. Unfortunately, even according to standards set by international organizations such as the International Union of Pure and Applied Chemistry (IUPAC), a chemical compound may have more than one correct, official name. Pharmacological compounds may be referred to by IUPAC chemical names, common names, and brand or product names and may also have pre-clinical laboratory designations. Identifying all the possible names a chemical may have is one major obstacle in a chemical search; fortunately, this can often be overcome by searching a compound’s CAS Registry Number, a 10-digit number assigned, by the Chemical Abstracts Service (CAS), to a known compound as a unique identifier of that material.
CAS Registry numbers are useful when searching in a CAS-produced database, such as REGISTRY, CAplus (patents and literature), or MARPAT, because all records in these files are intellectually indexed by the CAS staff with the appropriate compound numbers. In addition, performing an initial search using the CAS Registry number can illuminate common names and synonyms for a compound, which are listed in the REGISTRY file, a kind of "chemistry dictionary" which contains structure and physical property data for novel compounds that are published in patents or scientific journals. CAS Registry numbers are often used in technical documents to refer to the precise forms of the chemical compounds they mean to discuss. They represent an effective way to search on a known compound without having to account for potential variations in the name of that substance.
Registry number searches are especially effective when used in a database produced by CAS, such as the CAplus database, in which every patent and non-patent literature record is indexed by the CAS registry number of the compounds discussed in the document. There are some obstacles to CAS Registry number searching, however. First, Registry number searching does not work quite as well outside CAS-indexed data files. Without an indexing team to assign the numbers consistently, most databases cannot effectively search by these numbers. Not all patents use Registry numbers to describe the compounds they disclose, particularly if those compounds are novel and have not yet been indexed by CAS. Even within indexed files, Registry numbers are sometimes over-specific for the purposes of a given search: the specificity of CAS Registry numbers is such that a different registry number is assigned to every specific version of a known compound (for example, a different registry number would be assigned to each various salt of the same compound). This means that multiple Registry numbers might correspond to different versions of a chemical, but that all of these versions might be of interest to the searcher.
Finally, in addition to name and number searching, it is also possible to search for chemical substances through physical properties or molecular formulas. In the REGISTRY database, for example, partial chemical names can be combined with molecular formulas for broader retrieval. A list of databases that contain physical property information can be viewed in the non-patent literature section, below.
Chemical Structure Searching
Chemical name and registry number searching is acceptable when a known compound must be investigated. However, there are many situations where it is necessary to know whether a newly described chemical structure is already in the patent literature. For these kinds of investigations, an electronic chemical structure search is the best way to approach the problem. Several indexing services, such as Derwent, CAS and IFI, have produced electronic files which contain structure information that has been disclosed or claimed by patent documents, and which can actually be queried by chemical structure rather than keyword or classification code.
To understand how to use chemical structure search services, it is first necessary to understand how structure data is electronically indexed into these files. There are two distinct ways that chemical compounds are described in the patent literature. The first is when known structures are fully and specifically described in detail, such as in the following claims:
- 2. The method of claim 1 wherein said compound is alpha-phenyl-1-(2-phenethyl)-4-piperidine methanol.
- 3. The method of claim 1 wherein said compound is alpha-phenyl-1-(3-phenpropyl)-4-piperidine methanol.
This type of chemical information is exact, specific and can be easily translated into searchable electronic structure data.
The second way structure data is presented is when it is generically, partially, or broadly described in the patent literature. For example, this can be done by describing a list of different chemical fragments which may be substituted onto a defined backbone, or it may be as general as saying that a chemical could be made up of different but broadly described chemical components, such as an ester connecting two aliphatic groups, where the two groups can have many potential structures. Because similar chemical groups have related chemical behaviors, it is perfectly acceptable from a chemical standpoint to describe compounds this way, and legally, it has also been acceptable to claim such broadly defined chemical structures in a patent. Generically defined chemical structures are known in the industry as Markush patent claims. Below is an example of such a claim.
Because prior art searchers must take such broadly defined claims into account, there is a need for indexing services to translate this vague wording into an electronically searchable patent structure. Services which offer Markush structures as part of their searchable data necessarily must apply various indexing and editorial rules to determine how to effectively translate chemical ideas into electronic data. The various indexing rules used by these systems is beyond the scope of this discussion; however, what follows is a brief overview of the various data files and their collections.
- REGISTRY (CAS) – A dictionary of specific, known compounds and their structures associated with their unique CAS Registry number. Compounds are taken from worldwide patents from over 50 patent issuing authorities, and from over 10,000 leading chemistry journals, as well as other miscellaneous sources. The registry system was started in 1965, and the collection went online in the 1980s.
- MARPAT (CAS) – A file of generically indexed chemical structures from patents from over 50 patent issuing authorities, indexed by CAS, and begun in 1987.
- Merged Markush Service (MMS) (Derwent and INPI) – A collection built to index both specific and generic structures from patent documents in the Derwent World Patents Index (patents from "major" Derwent countries) and patents from the Pharm file (which contains bibliographic records from patents from US, EP, WO, DE, FR, GB authorities, as well as a French special medicine patents collection back to 1961). The specific structures in Derwent are referenced by their DCR (Derwent Chemical Resource) numbers, which can also be used to search for specific structures in the DWPI file outside of the MMS system. The MMS system has back-indexed many of its major countries back to 1978 and the French special medicine collection is searchable to 1961.
- Derwent World Patents Index (Derwent) – A patent family and bibliographic collection which began in the pharmaceutical industry in the 1960s, the Derwent World Patents Index has been indexed by a number of methods to make it searchable by chemical content. Generic structures can be searched by "linking" chemical fragmentation codes; this is a more rudimentary method than what is available in MARPAT or MMS, but the indexing extends farther back than those resources, to 1963. A special system to index polymers, Plasdoc is also included in the file and covers documents back to 1966 for some countries.
- IFI Claims® Compound Registry (IFI) – (The following paragraph is provided via the Dialog Bluesheet for this file as loaded on the Dialog platform from Thomson Reuters, accessed at http://library.dialog.com/bluesheets/html/bl0242.html on April 25, 2008:) "The CLAIMS®/Compound Registry database is a dictionary of specific chemical compounds produced by IFI Patent Intelligence. Each record contains the IFI compound term number, main compound name, synonyms, molecular formula, and fragment codes and terms. The file includes all specific compounds which have been referenced in the CLAIMS databases five or more times since 1950."
- ChemSpider – A free and computer-built database of chemical structure data on the web, ChemSpider searches patents and scientific journal articles as well as web content. It has partnered with patent database producer SureChem to provide some chemical patent content. This search engine relies on programs which read electronic data to deduce structure information. Structure coding keys such as InChi and SMILES are acceptable search criteria, as well as user-built graphical structure queries that can be drawn and uploaded to the service. This service sets itself apart because of its recent introduction and its machine-based indexing approach (as opposed to the other files which all rely on some measure of human indexing to tag records with appropriate chemical data). Although it is a free service, it is likely to give results of less quality than a service built on human indexing and curation.
Because these services are produced by different entities, they will have different coverage, and the chemical data in them will be treated by different indexing rules. This means the same query will produce different results in each database. It is always a good idea to carefully review the requirements of any search to make sure the most appropriate services are selected, and it’s always best to run the search in as many databases as possible.
In addition to selecting the appropriate database(s), chemical searching is also challenging due to the extra need for search training on these special tools. Because most of these structure search systems were developed at the very beginning of the computer age, most still operate on older technology platforms that are not always easy to use. In addition, the indexing methods in some of these systems may have changed over time and is no longer completely straightforward due to revisions and evolutions. In-depth training is required before users can become proficient on these complex systems, usually involving multiple sessions and practice problems. Complete mastery over the nuances of these systems is generally only attained by industry veterans, and is not something that can be developed over a few weeks. To complicate the situation further, the high cost of performing a chemical structure search can present an obstacle both to user comfort and proficiency, and also to the thoroughness and/or completeness of searches themselves.
A further obstacle to chemical structure searching is the need to appropriately allow generic features when defining a structure query. Most structure search engines allow variability in the search query as well as in the indexing criteria. Introducing variability into a structure query requires the technical know-how to use the system commands, the search instinct to understand whether the query has been defined too broadly or narrowly, and both the chemical and patent law knowledge to understand what possible variations of a structure will fall into the required legal scope of the search. If the search is defined too broadly, the results will be "noisy" and the display costs to view hit records will usually be quite high. If it is defined too narrowly, the user runs the risk of missing important prior art references that could cost the patent application, and ultimately in a corporate setting could cause huge sums of money to be wasted in a R&D effort.
In sum, the major obstacle to using chemical structure search databases is the peculiar and rare combination of technical know-how, search instinct, and chemical knowledge required to use them successfully. Because so much know-how and expertise is required to run a successful chemical structure search, novice searchers are best served by approaching the experts for help.
Because only a few, select databases are searchable by chemical structure, classification and keyword searching are always needed to round out a complete search for any molecular entity. A major obstacle here is identifying the appropriate patent classifications to investigate. Chemistry is covered by a large number of US and international classes, and searchers must identify all the proper classifications that could encompass the chemical compound of interest to ensure that the search is complete. For example, organic molecules and "body-treating" compositions can be classified by their use and/or by their chemical structure, and might be found in various US classes, including class 514, the 520 series, or the 532-570 series. Due to the sometimes disjointed nature of various classification systems, identifying all the subclasses that cover not only the chemical groups of a compound, but also the areas which may pertain to its indicated uses, can be challenging.
Polymeric compounds and non-pharmacological compounds such as metal alloys present other sets of challenges and must rely on combinations of classification, keyword, and structure searching.
Searching Patent Documents
Choosing a patent search system in this discipline should be influenced by the same coverage and search efficiency considerations that come into play during any type of patent search. Especially in keyword searching chemical names, it is beneficial to choose a search engine which allows unlimited left and internal truncation. Searches which may have a mechanical component, such as medical devices, may require image searching, and a tool which includes fast patent image load times is desirable. Due to the high-level of chemical indexing present in the Derwent World Patents Index file, it is also desirable to choose a patent search tool which includes that collection. See the articles on specific commercial patent search tools to learn more about each tool’s capability.
Any complete patent search will tap multiple resources. Regarding chemical structure searching, it is usually appropriate to make use of all possible resources, rather than attempting to choose one tool over another. Fortunately many major sources of chemical structure searching are available through one source: STN hosts the CAS REGISTRY file, the CAplus file, and the Markush structure file MARPAT. However, searching the Merged Markush Service (MMS), another important source for generic structure searching, can only be done through the Questel-Orbit host. Although chemical structure searching using these files can be cost-intensive, noted industry professionals agree that both the MARPAT and MMS systems should be queried in addition to Registry for a complete Markush structure search.
Free resources such as ChemSpider and Google Patent Search are attractive due to their low cost, but come at the expense of lower security. Any novel chemical structure, especially one with pharmaceutical properties, is likely highly confidential information, and using free web resources to investigate it should be considered with caution.
Searching Non-Patent Literature
Non-patent literature sources for chemical information include NCBI PubMed (which has access to MEDLINE) and PubChem, various databases on STN such as CAPlus, ChemSpider, and various specialized files available through multiple search hosts. NCBI’s PubChem Substance and PubChem Compound especially are good resources for identifying synonyms, common and product names, and registry numbers for known chemical substances of interest. Specialized files also exist which are compilations of literature related to a specific industry which relies on chemical innovations, such as Agricola (which relates to agriculture) and RAPRA (which is significant for the rubber and plastic industry). The following list provides just a brief overview of these major chemical literature sources and their content.
- CAplus (STN) - Probably the best known resource for chemical information. Contains select records from over 10,000 chemistry journals worldwide; contains complete cover-to-cover data for about 2,000 leading scientific journals. This file is chemical-structure-searchable when used in combination with the CAS REGISTRY database.
- ChemSpider – This free online resource collects chemistry structure and physical property data from dozens of web resources, among them the NIST Chemistry WebBook, PubChem, Thomson Pharma, Surechem patent data, and even Wikipedia, and aggregates all this data into a structure-searchable chemical database. In addition to graphical structures the system uses SMILES, InChI, and InChIKey codes to represent chemical structures. ChemSpider relies on user feedback to validate correct data and remove erroneous information from the records, which are machine-generated based on content culled from these various sources and thus are not as reliable as chemical registry databases created by human indexers.
- CHEMnetBASE – A collection of subscription services, including a structure-searchable file known as the Combined Chemical Dictionary, published by Chapman & Hall/CRC. The database includes "descriptive and numerical data on the chemical, physical and biological properties of compounds; systematic and common names of compounds; literature references; structure diagrams and their associated connection tables." The product is only available on an organization-wide subscription basis. The service also offers property databases for polymers and organic chemicals, as well as a searchable version of the CRC Handbook of Chemistry and Physics.
- DiscoveryGate – A commercial database produced by Elsevier MDL, DiscoveryGate provides access to a number of individual datafiles related to topics in pharmaceutical development, including medicinal chemistry, toxicity, molecular biology and compound bioactivity, and numerous files devoted to synthetic methodology. The service also includes resources related to chemical sourcing, so that drug developers can identify chemical suppliers.
- FDA Orangebook - The FDA orange book gives patent product protection information for pharmacological compounds that are approved for sale in the U.S. Similar resources exist for markets in other parts of the world like the Euro-zone. Searches that focus on pharmaceutical compounds should always begin by looking up the compound of interest to find its Orangebook entry and underlying patent protection.
- NCBI Pubmed – PubMed is a service of the U.S. National Library of Medicine that includes over 17 million citations from MEDLINE and other life science journals for biomedical articles back to the 1950s." PubMed includes links to full text articles and other related resources. PubMed is accessed through Entrez, a gateway that also accesses a number of databases of genetic sequence information, 3D protein structures, and small molecules databases (such as PubChem, discussed further below).
- NIST Chemistry WebBook – This portal provides free access to chemical structure and property data compiled by the National Institiute of Science and Technology (NIST). It contains IR and mass spectra, UV/vis data, gas chromatography data, electronic and vibrational spectra, ion energetic data, diatomic constants, thermochemistry and reaction thermochemistry data, and thermophysical property data for thousands of known compounds. The database can be searched by name, chemical formula, CAS registry number, molecular weight, chemical structure, or selected ion energetics and spectral properties.
- PubChem – A chemical structure-searchable database of information regarding the biological activity of small molecules. The portal can access PubChem Substance, Compound, and Bioassay data collections. The PubChem databases can be accessed for free via the NCBI Entrez portal.
- Thomson Pharma - A commercial database of literature and reports related to the drug discovery and development process.
Some specialized industry-focused files that include information related to chemical innovations include:
- Agricola (Dialog, STN) – A database of agricultural information that contains information on food science, fertilizers and soil science, as well as biotechnology topics including transgenic plants. Multilingual source materials include books, pamphlets, conference proceedings, translations, book chapters, research reports, etc. ([Dialog Bluesheet])
- Ceramic Abstracts/World Ceramics Abstracts (CERAB)(STN) - The CERAB database is produced by Cambridge Scientific Abstracts (CSA), and contains "records from the scientific, commercial, and engineering literature on traditional and advanced ceramics and related materials, including their properties, processing, testing, applications, and manufacture." (STN Database Summary Sheet)
- Chemical Engineering and Biotechnology Abstracts (CEABA)(Dialog, STN) - References from 500 core journals, and some books, technical reports, and some press releases and conferences. (Dialog Bluesheet)
- PaperChem (Dialog and STN) – Directed to the pulp and paper industry, including materials on chemicals related to the industry (another file directed to the paper industry, PIRA, is also available on Dialog and STN but seems to have less of a chemistry emphasis.) (Dialog Bluesheet)
- Polymer Online (Dialog) – "Polymer Online contains the full text of Wiley's Encyclopedia of Polymer Science and Engineering, 2nd edition, 17 volumes, Supplement, and cumulative index. The Encyclopedia contains approximately 600 articles (chapters) written by contributors who are experts in their fields. The articles include over 3,000 tables, 3,000 figure titles, and six million words of text." (Dialog Bluesheet)
- RAPRA Rubber and Plastics (Dialog, STN, Questel) - dedicated exclusively to rubbers, plastics, adhesives, and polymeric composites. The Dialog data sheet states that "the database comprises a large collection of carefully produced, extensively indexed summaries covering a wide range of subjects encompassing technical, academic, commercial, and marketing aspects of the rubber and plastics industries." (Dialog Bluesheet)
This list is partial and intended to exemplify the kind of specialized resources that exist for commercial areas. Many other resources for specialized fields of chemistry exist outside of these selected resources and should be sought out by the searcher. See our Resource Finder tool for an extended list of files relevant to chemical searching.
Search Strategies Specific to the Subject Area
These search strategies are examples of specific best practices that can be applied during the course of a search in the area of chemistry/pharmaceuticals searching. These are steps to be taken in addition to accepted search practices that apply to all searches. For a more general progression of search steps, please see the General Searching best practices article.
Determine whether the search subject matter warrants a chemical structure search on a novel chemical compound. If the search does require a structure search, consider the following steps:
- Review structure searching resources and search requirements to select the appropriate database(s). It cannot be stressed enough that for most searches of this type, every possible resource should be consulted. Generally, in addition to substructure-searching in CAS REGISTRY-style databases of known compounds, generic structure databases MARPAT and MMS should be consulted, and if possible chemical fragmentation codes should be used to search the Derwent World Patents index.
- Using both 1) the description of the search goals and scope as communicated by the requester, and 2) the searcher’s own chemical knowledge, define the structure query to be searched. This may involve removing known functional groups from a molecular structure and replacing them with generic variable group codes as permitted by the selected search engine to broaden the query, such as replacing a "Cl" atom with a marker that would permit any halogen atom at that site. It could also involve applying abstract "translation" or "match level" values to certain sites or groups on the structure to tell the search engine how broadly it should interpret the query. If the search engine does not permit graphical query input, write or type out the command language needed to input the chemical structure parameters into the system.
- Consult the search recipient again after defining the query, if possible, to ensure that the query has been defined appropriately without excluding desirable structures from the query, or being overly-inclusive.
- Consult a colleague proficient in structure searching, or the search system helpdesk, to double-check that the structure query has been correctly defined from a chemical and searching standpoint. Clear up any questions about the query creation tools or about how the system will interpret a certain query before running the search.
- Use cost-saving tips and tricks, such as using the CASlink option in STN, which searches both CAplus and MARPAT simultaneously for a discounted search.
Determine whether the search is to be performed on a known drug or formulation of a drug. If so, consider the following steps:
- Consult the FDA Orangebook to learn which assignee(s) own patents for the drug, and examine the patent numbers for those drugs to identify classes and subclasses relevant to the search.
- Use "chemistry dictionary" databases, such as the free resources PubChem Compound/PubChem Substance, and pay resources such as CAS REGISTRY, to identify alternate names for the drug. (Any alternate names discovered using a text-mining database such as Chemspider or SureChem should be verified before use in a search).
- Use text queries as a primary search strategy to perform investigations on all known alternative drug names.
- Use classification searching as a secondary search method for thoroughness.
Key Classification Areas
|008||Bleaching and dyeing; fluid treatment and chemical modification of textiles and fibers|
|023||Chemistry: physical processes|
|044||Fuel and related compositions|
|075||Specialized metallurgical processes, compositions for use therein, consolidated metal powder compositions, and loose metal particulate mixtures|
|106||Compositions: coating or plastic|
|156||Adhesive bonding and miscellaneous chemical manufacture|
|162||Paper making and fiber liberation|
|204||Chemistry: electrical and wave energy|
|208||Mineral oils: processes and products|
|260||Chemistry of carbon compounds (See 532-570 series)|
|420||Alloys or metallic compositions|
|422||Chemical apparatus and process disinfecting, deodorizing, preserving, or sterilizing|
|423||Chemistry of inorganic compounds|
|424||Drug, bio-affecting and body treating compositions|
|428||Stock material or miscellaneous articles|
|429||Chemistry: electrical current producing apparatus, product, and process|
|430||Radiation imagery chemistry: process, composition, or product thereof|
|435||Chemistry: molecular biology and microbiology|
|436||Chemistry: analytical and immunological testing|
|502||Catalyst, solid sorbent, or support therefor: product or process of making|
|504||Plant protecting and regulating compositions|
|506||Combinatorial chemistry technology: method, library, apparatus|
|510||Cleaning compositions for solid surfaces, auxiliary compositions therefor, or processes of preparing the compositions|
|514||Drug, bio-affecting and body treating compositions|
|516||Colloid systems and wetting agents; subcombinations thereof; processes of|
|518||Chemistry: fischer-tropsch processes; or purification or recovery of products thereof|
|520||Synthetic resins or natural rubbers - part of the class 520 series|
|521||Synthetic resins or natural rubbers - part of the class 520 series|
|522||Synthetic resins or natural rubbers - part of the class 520 series|
|523||Synthetic resins or natural rubbers - part of the class 520 series|
|524||Synthetic resins or natural rubbers - part of the class 520 series|
|525||Synthetic resins or natural rubbers - part of the class 520 series|
|526||Synthetic resins or natural rubbers - part of the class 520 series|
|527||Synthetic resins or natural rubbers - part of the class 520 series|
|528||Synthetic resins or natural rubbers - part of the class 520 series|
|530||Chemistry: natural resins or derivatives; peptides or proteins; lignins or reaction products thereof|
|532||Organic compounds - part of the class 532-570 series|
|534||Organic compounds - part of the class 532-570 series|
|536||Organic compounds - part of the class 532-570 series|
|540||Organic compounds - part of the class 532-570 series|
|544||Organic compounds - part of the class 532-570 series|
|546||Organic compounds - part of the class 532-570 series|
|548||Organic compounds - part of the class 532-570 series|
|549||Organic compounds - part of the class 532-570 series|
|552||Organic compounds - part of the class 532-570 series|
|554||Organic compounds - part of the class 532-570 series|
|556||Organic compounds - part of the class 532-570 series|
|558||Organic compounds - part of the class 532-570 series|
|560||Organic compounds - part of the class 532-570 series|
|562||Organic compounds - part of the class 532-570 series|
|564||Organic compounds - part of the class 532-570 series|
|568||Organic compounds - part of the class 532-570 series|
|570||Organic compounds - part of the class 532-570 series|
|585||Chemistry of hydrocarbon compounds|
|Section C - Chemistry; Metallurgy|
|C08||Organic Macromolecular Compounds; Their Preparation Or Chemical Working-Up; Compositions Based Thereon|
|C09||Dyes; Paints; Polishes; Natural Resins; Adhesives; Compositions Not Otherwise Provided For; Applications Of Materials Not Otherwise Provided For|
|C10||Petroleum, Gas Or Coke Industries; Technical Gases Containing Carbon Monoxide; Fuels; Lubricants; Peat|
|C11||Animal Or Vegetable Oils, Fats, Fatty Substances Or Waxes; Fatty Acids Therefrom; Detergents; Candles|
|C12||Biochemistry; Beer; Spirits; Wine; Vinegar; Microbiology; Enzymology; Mutation Or Genetic Engineering|
|C25||Electrolytic Or Electrophoretic Processes; Apparatus Therefor|
|IPC - USPC Concordance|
|A61K||Concordance with 424 and 514 for body treating methods and compositions.|
|A01N||Concordance with 424, 514 and 504 for disinfectants and biocides, treating plants.|
|A61P||Concordance with 424 and 514 as a discretionary IPC for treatment utility if A61K is assigned.|
|A01P||Concordance with 424, 514 and 504 as a discretionary IPC for treatment utility if A01N is assigned.|
Since chemistry and pharmaceutical searches sometimes require a certain level of sophistication beyond picture image searching, chemistry searchers may also need to familiarize themselves with some mechanical engineering concepts and medical devices nomenclature. Searchers may also need to become familiar with sequence searching for specific nucleic acid and peptide molecules alone or in combination with other chemical engineering processes and materials. For further reading, searchers should reference the corresponding best practices articles covering mechanical engineering, medical devices, and chemical engineering. Due to some overlap in the fields, the best practices and sources disclosed in those articles may also be applicable to chemistry and pharmaceutical searches.
- ↑ Austin, Robert. "The Complete Markush Structure Search: Mission Impossible?" Presented at the PIUG NE Workshop, October 16th, 2001. STN website, http://www.stn-international.de/training_center/chemistry/piug1.pdf. Accessed on January 28, 2008.