US PATENT SUBCLASS 540 / 45
.~.~.~.~.~ The spiro hetero ring is four-membered consisting of one oxygen and three carbons

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540 /   HD   ORGANIC COMPOUNDS -- PART OF THE CLASS 532-570 SERIES

*  DD  ORGANIC COMPOUNDS (Class 532, Subclass 1) {1}
1  DF  .~ HETEROCYCLIC CARBON COMPOUNDS CONTAINING A HETERO RING HAVING CHALCOGEN (I.E., OXYGEN, SULFUR, SELENIUM OR TELLURIUM) OR NITROGEN AS THE ONLY RING HETERO ATOMS {6}
2  DF  .~.~ Cyclopentanohydrophenanthrene ring system containing {10}
6  DF  .~.~.~ Spiro {3}
28  DF  .~.~.~.~ The spiro includes the cyclopentanohydrophenanthrene ring system and a hetero ring {6}
45.~.~.~.~.~ The spiro hetero ring is four-membered consisting of one oxygen and three carbons

DEFINITION

Classification: 540/45

(under subclass 28) Compounds in which the spiro hetero ring is four-membered consisting of one oxygen and three carbons.

(1) Note. An example of a compound provided for herein is: [figure]