Drugmaker Shire (SHP.L) said on Tuesday it was seeking to buy Baxalta (BXLT.N), a company spun-off by Baxter International (BAX.N) last month, for $30 billion to forge the leading global specialist in rare diseases. Baxalta rebuffed the offer on Tuesday and said in a statement that Shire’s unsolicited offer significantly undervalued the company. Shire’s all-share offer values each Baxalta share at $45.23, based on Aug. 3 market prices.