| 544 / | 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) {1} | 
| 1 | DF | .~.~ Hetero ring is six-membered having two or more ring hetero atoms of which at least one is nitrogen (e.g., selenazines, etc.) {6} | 
| 3 | DF | .~.~.~ Six-membered hetero ring consists of oxygen, sulfur, nitrogen and carbon (e.g., oxathiazines, etc.) {7} | 
| 5 |  | .~.~.~.~ Plural sulfurs in the six-membered hetero ring (e.g., dithiazines, etc.) |