Charles Best, founder of the New York-based nonprofit DonorsChoose, sat in his garment district office yesterday and contemplated the loss of his biggest corporate benefactor after the bankruptcy of Lehman Brothers Holdings Inc.

The Lehman Brothers Foundation gave DonorsChoose $500,000 each of the past three years, or 7 percent of its most recent operating budget. It pledged another $500,000 for 2009. Best said the money was key to the national expansion of his 8-year-old organization, which enables individuals to fund projects proposed by public school teachers.