Rajan Kundra, a proprietary interest-rate derivatives trader at Lehman Brothers in New York, has left the firm. He is not thought to have joined a competitor, according to officials. Kundra joined Lehman in 2001 and moved to his latest prop trading position after having worked as a corporate interest-rate derivatives marketer, added the officials. Kundra could not be reached. Kerrie Cohen, spokeswoman in New York, did not return calls.