| 552 / | HD | ORGANIC COMPOUNDS -- PART OF THE CLASS 532-570 SERIES |
| * | DD | ORGANIC COMPOUNDS (Class 532, subclass 1) {11} |
| 500 | DF | .~ Cyclopentanohydrophenanthrene ring system wherein two nonadjacent carbons of the ring system are bonded directly to each other (e.g., 3,5 cyclocholesterols, 3,5-cycloandrostanes, etc.) {1} |
| 501 | | .~.~ Oxygen bonded directly at the 6-position of the cyclopentanohydrophenanthrene ring system |