Alexion’s Acquisition of Synageva

Alexion Pharmaceuticals will buy rival Synageva BioPharma in an $8.4 billion cash-and-stock deal that will bolster Alexion’s business in treatments for rare diseases.

Alexion’s takeover offer is aggressive: It will pay $115 in cash and 0.6581 Alexion shares for each share of Synageva, amounting to $230 in cash and stock.