GlaxoSmithKline has revealed plans to sell 450m pounds of shares in Africa's largest drug company, Aspen Pharmaceutical.GSK said it wanted to offload around a third of its 19% stake in Johannesburg-listed Aspen, which is currently valued at 122bn rand, equivalent to £7.5bn.The 6% of sold shares would be worth around £450m at the current price, with the offer price to be determined by means of an accelerated bookbuild process starting immediately by Citigroup and UBS, with GSK's retained 13% stake in Aspen worth almost £1bn. The FTSE 100 company said proceeds of the divestment will not be included in core operating profit and core EPS in 2013 and the cash will be used for general purposes.GSK said its close relationship with Aspen and current transactions between the companies will not be affected by this transaction, and that it would retain a seat on Aspen's board.David Redfern, GSK's Chief Strategy Officer, said: "GSK has a long and successful partnership with Aspen - and our investment in the company has grown in value significantly over time. Having assessed this investment we have now decided to realise some of this value without altering the basis of the partnership."Shares in GSK were up 1.2% to 1,634p at 15:35 on Tuesday.OH