Complex sentence: Pranab Mukherjee was stated to be too critical at his current responsibility to stand for the Presidential elections and the Left parties opposed the candidature of Shivaraj Patil, Sushil Kumar Shinde and Karan Singh.
Split into simpler sentences: Pranab Mukherjee was stated to be too critical at his current responsibility to stand for the Presidential elections. However, the Left parties were opposed to the candidature of Shivaraj Patil, Sushil Kumar Shinde and Karan Singh.