Syngenta (SYT) shares were on watch as the company reportedly builds its defenses against another potential takeover bid from Monsanto (MON). The agricultural company had added UBS (UBS) as its advisor alongside Goldman Sachs (GS) as it prepares for a higher bid than the $45 billion offer it previously rejected. Stocks were trading slightly lower on the final trading day of May. A revised GDP reading for the first quarter showed the U.S. economy shrank, while a potential Greek exit of the eurozone continued to pressure global markets. Software developer Splunk (SPLK) tumbled despite reporting a narrower-than-expected net loss.