Weakening overseas demand for US soybeans also weighed on prices.
Traders noted some unwinding of bull spreads as the closely watched July-November spread neared its all-time high before giving up 3-1/2 cents during Wednesday's session.
Although most soybean contracts closed lower, CBOT May , which is in the delivery period, rose 4-3/4 cents. The thinly traded front-month contract peaked at it highest since July 12, 2013 during the session.
Analysts were expecting a weekly US Agriculture Department report on Thursday morning to show old-crop soybean export sales in range from -250,000 to 100,000 tonnes. New-crop sales were forecast between 250,000 to 450,000 tonnes.
Soymeal futures remained firm as tight supplies lent support. Dealers on the cash market said demand was routine but more maintenance shutdowns were expected in the coming weeks, which will keep a bullish tone on prices.
Weakness in crude oil prices weighed on soyoil futures, which fell 1.9 percent. The benchmark July soyoil contract fell below its 40-day and 50-day moving averages but closed above its 30-day moving average.