| 549 / | HD | ORGANIC COMPOUNDS -- PART OF THE CLASS 532-570 SERIES | 
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| * | DD | ORGANIC COMPOUNDS (Class 532, Subclass 1) {1} | 
| * | DD | .~ HETEROCYCLIC CARBON COMPOUNDS CONTAINING A HETERO RING HAVING CHALCOGEN (I.E., OXYGEN, SULFUR, SELENIUM, OR TELLURIUM) OR NITROGEN AS THE ONLY RING HETERO ATOMS (Class 540, subclass 1) {2} | 
| 200 | DF | .~.~ Oxygen containing hetero ring (e.g., dioxirane, etc.) {16} | 
| 263 | DF | .~.~.~ Lactones (i.e., -C(=X)O-, wherein X is chalcogen, is part of the hetero ring) {6} | 
| 295 | DF | .~.~.~.~ The lactone ring is five-membered {10} | 
| 297 | DF | .~.~.~.~.~ Polycyclo ring system having the lactone ring as one of the cyclos {3} | 
| 302 | DF | .~.~.~.~.~.~ Bicyclo ring system having the lactone ring as one of the cyclos {6} | 
| 304 |  | .~.~.~.~.~.~.~ Nitrogen attached indirectly to the lactone ring by acyclic nonionic bonding |