UPDATE 2-Astellas to get limited look at OSI's books

* Astellas gets access to some OSI nonpublic information

* OSI board rejected Astellas takeover offer on March 15

(Adds details; share price)

NEW YORK, March 29 (Reuters) - Japan's Astellas Pharma Inc 4503.T, which is pursuing a $3.5 billion hostile takeover of OSI Pharmaceuticals Inc OSIP.O, said on Monday it would gain a partial look at the financial records of OSI.

Under the confidentiality agreement, OSI will provide Astellas with access to certain nonpublic information. In return, Astellas, Japan’s drugmaker, will not acquire any shares of OSI under its tender offer until May 15.

Moreover, it also prohibits Astellas from taking any further action on its pending litigation or to file a preliminary or definitive proxy statement in connection with OSI’s annual meeting.

OSI said the move to open its books to Astellas “reflects our board’s prior commitment to explore the availability of a transaction that reflects the full intrinsic value of our company,” OSI said.

The move was consistent with the “basic provisions” it has offered other parties. It did not elaborate on whether it was in talks with any other suitors.

OSI’s board rejected Astellas’s takeover offer on March 15 and instructed management to look for deals with other parties.

OSI said no assurance could be given on whether any deal would emerge. A deal for OSI would boost Astellas’ oncology presence by giving it rights to the blockbuster Tarceva cancer drug.

Earlier this month, Astellas unveiled a full proposed slate of directors to vie for control of OSI’s board.

OSI shares closed on Monday at $59.30. OSI’s stock has traded well above the $52-per-share offer as investors expect either a higher price or another suitor. (Reporting by Ransdell Pierson in New York and Jessica Hall in Philadelphia)