disulfides or other sulfur species were not formed. These methods may also be useful in the preparation of calicheamicin conjugates and other derivatives required for its clinical applications. C) The formation of the methylbenzyl trisulfide co-product was confirmed by GC-MS. D) H NMR data highlighting the key changes resulting from the S-S metathesis reaction. The methyl group from the material was no longer observed, as it was transferred to the methylbenzyl trisulfide co-product. The benzylic peaks of the modified calicheamicin g1 were clearly observed.