Tetrahydrobacteriochlorins and Isobacteriochlorins

It is now accepted that the reduced double bond in chlorins induces a pathway for the delocalized n electrons that isolates the diagonal cross-conjugated pyrrolic double bond, such that reduction of this double bond is favored due to minimal loss of % energy over the double bond present in the adjacent. The presence of a metal changes the delocalization of the n electrons, which makes the adjacent pyrrolic ring more reactive, and diimide reduction produces mainly the corresponding isobacteriochlorins. 

The diimide-reduction approach was later employed by Bonnett et al. for preparing the /Mcso-tetra(m-hydroxyphe-nyl)-bacteriochlorin H2(m-THPBC). In vivo biological assays of mmor response showed that H2(m-THPBC) was a very active tumor photosensitizer. However, it was relatively unstable when compared with H2(m-THPC) in vitro. About 25 to 33% of the H2(m-THBPC) within the cells was oxidized to chlorin in 24 hours.  

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