Stereoselective activation of dibenzo[<i>a,l</i>]pyrene to (—)-<i>anti</i>(11<i>R</i>, 12<i>S</i>, 13<i>S</i>, 14<i>R</i>)- and (+)-<i>syn</i>(11<i>S</i>, 12<i>R</i>, 13<i>S</i>, 14<i>R</i>)- 11, 12-diol-13, 14-epoxides which bind extensively to deoxyadenosine residues of DNA in the human mammary carcinoma cell line MCF-7