| 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} | 
| 224 | DF | .~.~.~ The six-membered hetero ring consists of two nitrogens and four carbons (e.g., 1,2-diazines, etc.) {9} | 
| 336 | DF | .~.~.~.~ 1,4-diazines {9} | 
| 358 | DF | .~.~.~.~.~ Piperazines (i.e., fully hydrogenated 1,4-diazines) {12} | 
| 359 | DF | .~.~.~.~.~.~ Additional hetero ring containing {4} | 
| 374 | DF | .~.~.~.~.~.~.~ Ring chalcogen in the additional hetero ring {2} | 
| 375 | DF | .~.~.~.~.~.~.~.~ Polycyclo ring system having the additional hetero ring as one of the cyclos {2} | 
| 376 |  | .~.~.~.~.~.~.~.~.~ Bicyclo ring system having the additional hetero ring as one of the cyclos {1} | 
| 377 | DF | .~.~.~.~.~.~.~>.~.~.~ Plural ring chalcogens in the bicyclo ring system |