Australia-listed software maker Altium Ltd (ALU.AX) on Monday rejected a buyout proposal from American peer Autodesk Inc (ADSK.O) that valued the company at A$5.05 billion ($3.91 billion), saying it "significantly undervalued" its prospects. The U.S. firm, which makes architecture designing software AutoCAD, offered Altium A$38.50 for each share, a 41.5% premium to its last closing price. Altium"s shares soared as much as 40.6% to mark their biggest intraday gain in more than a decade before pulling back to trade 34.7% higher. The proposal followed talks of a strategic partnership between the two companies, with Autodesk looking to integrate Altium"s electronics designing software with its engineering and manufacturing software platforms to provide its users a host of applications under one cloud network. San Diego, California-based Altium said it "rejects the proposal at the current price", adding it would engage with interested parties for an appropriate valuation and pursue a review of all potential strategic alternatives. Autodesk, which is also based in California, did not immediately respond to a request for comment on the rejection. ($1 = 1.2923 Australian dollars)