Complex sentence: The Metropolitan Museum and the Guggenheim Museum did not comply, although, under pressure from the AWC, the Metropolitan did postpone the opening of its American painting and sculpture show scheduled for that day, while the Guggenheim was picketed.
Split into simpler sentences: The Metropolitan Museum and the Guggenheim Museum did not comply. Under pressure from the AWC, the Metropolitan did postpone the opening of its American painting and sculpture show scheduled for that day, while the Guggenheim was picketed.