Ligand Pharmaceuticals Inc. (LGND, $2.54, -$0.22, -7.97%) announced plans to buy cash-strapped drug developer Neurogen Corp. (NRGN, $0.20, +$0.00, -0.15%) for $11 million in stock plus the potential for millions more in cash, giving Ligand access to a partnership with Merck & Co. (MRK, $32.50, -$0.06, -0.18%).