Patent 5247090 Issued on September 21, 1993. Estimated Expiration Date: January 21, 2013. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
546/89, Ring oxygen in the tricyclo ring system544/126, The additional six-membered hetero ring is one of the cyclos in a tricyclo ring system546/92Plural chalcogens bonded directly to ring carbons of the tricyclo ring system