An investors group headed by Minneapolis businessman Irwin L. Jacobs said it bought more than 3 million shares of common stock in Honolulu-based Castle & Cooke Inc. "We obviously have an interest, because it's undervalued," Jacobs said. "We are looking at it as an investment, or with the possibility of a takeover move." Jacobs said the purchase amounted to more than 12% of Castle & Cooke's outstanding shares. The stock closed Thursday at $16 a share, up 12.5 cents. The day before it rose $2 to $15.875.