US drugmaker AbbVie raised its offer for London-listed hyperactivity and rare diseases specialist Shire to 30.1 billion pounds ($51.3 billion) on Tuesday, hoping to win over its reluctant target after three earlier offers were rejected.

The latest 51.15 pounds a share cash-and-stock offer is 11 percent higher than AbbVie’s previous proposal of 46.26 pounds, which Shire had said fundamentally undervalued the company.

AbbVie is eager to buy Shire both to reduce its tax bill by moving its tax base to Britain - a tactic known as inversion - and to diversify its drug portfolio. The US company currently gets nearly 60 per cent of its revenue from rheumatoid arthritis drug Humira, the world's top-selling medicine, which loses US patent protection in late 2016.

Chief executive Richard Gonzalez has pressed the case for his pursuit of Shire in a series of meetings with shareholders on both sides of the Atlantic, after setting out the strategic rationale for a deal on June 25.
 
AbbVie said it had now met with, or spoken to, a large number of Shire investors, who collectively represented a majority of Shire’s shares.

It is the second attempt by a US pharmaceutical company to buy a London-listed rival, after Pfizer's $118 billion pursuit of AstraZeneca failed last month.-Reuters