Sigma announced it has entered into a confidentiality agreement with Aspen Pharmacare Holdings Ltd, providing access to the company's due diligence information.

"As part of that agreement, Aspen has been granted limited exclusivity by Sigma for the next four weeks, during which period Sigma has agreed not to solicit rival bids for another whole of business transaction for Sigma, or to enter into contracts in relation to asset sales. However, Sigma is continuing the previously foreshadowed asset sale program," said Sigma general counsel and company secretary Sue Morgan-Dethick in a statement to the ASX.

Aspen Pharmacare has made a $07 million non-binding, indicative and conditional offer to buy Sigma at $0.60 per share under a scheme of arrangement or other whole of business transaction.

Sigma recommends that shareholders take no action at this time in relation to the indicative proposal as the due diligence process being undertaken by Aspen may or may not result in a formal proposal or a recommendation by the Board.

Last month, Sigma chief executive Elmo de Alwis resigned in the wake of criticism after the company reported a massive $389 million loss for the year to January 31, 2010. His resignation was followed by Sigma chief financial officer Mark Smith.

Sigma chairman Dr. John Stocker announced his retirement following the company's annual general meeting on June 21. Non-executive director Doug Curlewis has also decided to leave the board after the meeting.