| 546 / | 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 consisting of one nitrogen and five carbons {24} |
| 268.1 | DF | .~.~.~ Additional hetero ring containing {4} |
| 268.4 | DF | .~.~.~.~ The additional hetero ring is five-membered having two or more ring hetero atoms of which at least one is nitrogen {9} |
| 271.4 | DF | .~.~.~.~.~ 1,3-oxazoles (including hydrogenated) {1} |
| 271.7 |  | .~.~.~.~.~.~ Polycyclo ring system having the 1,3-oxazole ring as one of the cyclos |