A U.S. patent research group says it has uncovered evidence that could be used to declare AstraZeneca Plc's patent for its cholesterol fighter Crestor invalid.

AstraZeneca is involved in litigation to defend the Crestor patent from generic drugmakers that want to bring a cheaper copy to the U.S. market.

The patent group, Article One Partners LLC, did not say who found the prior art, essentially information describing the patented technology that dates from before the patent application. Discovery of good prior art would make defending a patent considerably more difficult.

Article One said the person is eligible to win an award of up to $50,000.

A similar discovery by Article One, launched by CEO Cheryl Milone last year, led to a patent office decision last month to reexamine a patent for Merck and Co Inc's blockbuster Singulair asthma and allergy drug.

Article One encourages researchers and experts in various fields to identify evidence related to patent validity. Those who succeed are paid and the collected evidence is sold to the group's clients.

(Reporting by Diane Bartz; editing by Andre Grenon)