Did you know you can use ring search terms in REGISTRY to help you answer questions about rings?
These terms are especially useful for:
- Specifying general information about rings that often appears in patent claims, for example, a heterocycle containing three nitrogen atoms
- Creating subsets for ring searches that exceed system limits when run as a substructure search
The following information provides an overview of searching ring systems based on information that you know about the rings.
Terminology
Let’s start by clarifying terms used to generate ring search data in REGISTRY:
- Ring systems
- Smallest set of smallest rings (SSSR)
- Hill system order
- Multicomponent substances
Ring Systems and Smallest Set of Smallest Rings
To explain ring systems and SSSR, let’s use this substance as an example:
This substance contains two ring systems:
- The upper ring system is named naphthalene.
- The lower ring system is named anthracene.
The SSSR for the naphthalene ring system is simply the set of two 6-membered C6 rings. The 10-membered C10 envelope ring is not counted.
The SSSR for the anthracene ring system is the set of three 6-membered C6 rings. The 14-membered C14 and the two 10-membered C10 envelope rings are not counted.
Hill System Order
Hill system order is used to represent ring system formulas. The rules for carbon-containing substances are:
- Number of carbons first
- All other elements in alphabetical order
For substances not containing carbon, elements are placed in alphabetical order. The substance above consists of two rings: C10 and C14. Hydrogens are not included.
Multicomponent Substances
Multicomponent substances are substances that consist of more than one component. For example, the mixture of aspirin, phenacetin, and caffeine is structured in REGISTRY as a multicomponent substance. The Ring System Data (RSD) is associated with each component
Searching for Ring Systems Completely Defined by the Specified Small Rings
The following table provides an overview of how you can search for ring systems consisting only of the specified rings. Using these fields can be very helpful if you need to do a broad sweep of the database to locate substances that contain all possible ring systems composed of a set of small rings.
| When you know about the small rings in a ring system... | Do this... | In this search field... | Examples |
| Elemental ring formulas |
Arrange formulas in Hill system order and ascending ring size. Precede by number of occurrences, if available. |
/EA (Elemental Analysis of a Ring System) |
S C5-C4N2-C6/EA S 2-4 C3S2/EA |
|
Atom sequences |
Arrange in order of ascending ring size and start with lowest alphabetical heteroatom. Precede by number of occurrences, if available. |
/ES (Elemental Sequences for a Ring System) |
S C5-NC2NC2-C6/ES |
| Ring sizes |
Arrange in ascending order. Precede by number of occurrences, if available. |
/SZ (Sizes of the Rings in a Ring System) |
S 6-6-18/SZ S 2-4 5/SZ |
Example Use Case 1
Locate substances containing only the rings defined as follows:
- 2 carbons and 1 oxygen
- 5 carbons
- Two rings of 6 carbons
- 6 carbons and 1 oxygen
Searching for Ring Systems Partially Defined by the Specified Small Rings
Searches in the /SZ, /EA, and /ES fields retrieve only ring systems containing the specified set of small rings. They do not retrieve ring systems in which those small rings are part of larger ring systems. Use the following search fields if you wish to allow other rings in the ring system.
| When you know about some of the smallest rings in a ring system... | Do this... | In this search field... | Examples |
| Elemental ring formulas |
Arrange formulas in Hill system order and ascending ring size. Precede by number of occurrences, if available. |
/EAS (Elemental Analysis for Some of the Smallest Rings) |
S C12O6/EAS S 2 C4N2/EAS |
|
Atom sequences |
Arrange in order of ascending ring size and start with lowest alphabetical heteroatom. Precede by number of occurrences, if available.
|
/ESS (Elemental Sequences for Some of the Smallest Rings) |
S 2 NC2NC2/ESS |
| Ring sizes | Arrange in ascending order. Precede by number of occurrences, if available. |
/SZS (Size of Some of the Smallest Rings) |
S 18/SZS S 2-3 5/SZS |
Proximity operators for ring searching include:
- (P) – In a single-component substance or one component of a multicomponent substance
- (S) – In the same ring system
Example Use Case 2
Locate ring system containing at least:
- 3-membered ring
- ring containing 5 carbons
- two rings containing 6 carbons
- ring containing 6 carbons and 1 oxygen
Searching Ring Elements for a Ring System
You can also describe and search the ring systems simply in terms of the elements of which they are composed.
| When you know... | Do this... | In this search field... | Examples |
|
All ring elements and their counts |
Arrange elements in Hill system order. Precede with the number and a space, if you know the number of occurrences |
/RF (Ring Formula) |
S C19O2S/RF S S8/RF |
|
All ring elements but not their counts |
Arrange the elements in Hill system order and separate by spaces. |
/RELF (Ring Elemental Formula) |
S C O S/RELF S 1 CL PT/RELF |
|
Some of the elements in a ring system |
Enter element symbols for the elements, including M = any metal, X = any halogen, Q = any non-carbon atom. If available, include a count of the number of occurrences and a space before the element. |
/REL (Ring Element) |
S 2-3 M/REL S (M(S)X)/REL S >8 S/REL |
| Number of unique ring elements |
Enter a number or use numeric operators. |
/RELC (Ring Element Count) |
S 7/RELC |
|
Total number of ring atoms |
Enter a number or use numeric operators. |
/RATC (Ring Atom Count) |
S 18/RATC S C/RELF(S)RATC>6 |
Example Use Case 3
Locate ring systems that:
- Contain 7-10 ring atoms and 3 ring nitrogens in the same ring system
- Any number of ring carbons and sulfurs
Search includes proximity operators (S) and (P)
Searching Ring Counts
You can also search the number of ring systems or smallest rings.
| When you know... | Search in this field... | Examples |
| Total number of ring systems in a substance |
/NRS (Number of Ring Systems) |
S 7/NRS |
| Number of ring systems in a single component of a substance |
/CNRS (Number of Ring Systems in a Single Component) |
S 3-4/CNRS |
| Total number of smallest rings in a substance |
/NR (Number of Smallest Rings) |
S M/REL AND 5-9/NR |
|
Number of smallest rings in a single component of a substance |
/CNR (Number of Smallest Rings in a Single Component) |
S 7/CNR |
|
Number of smallest rings in a ring system |
/NRRS (Number of Rings in a Ring System) |
S C/RELF(S) NRRS>20 |
| To require at least one ring system | RSD/FA |
S L1 AND RSD/FA |
|
To specify no rings in the substance |
NO RSD/FA |
S L1 AND NO RSD/FA |
Example Use Case 4
Find ring systems that contain:
- One metal
- 5-6 rings