Abstract
The synthesis of the central tryptophan residue of celogentin C is described featuring a Pd-catalyzed imine/enamine Heck-type reaction, a Pd-catalyzed Suzuki coupling, and an asymmetric Rh-catalyzed hydrogenation.
Key words
asymmetric catalysis - palladium - rhodium - natural products - total synthesis
References and Notes
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[2 3
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24 In examples described in the literature, asymmetric hydrogenations with (S ,S )-MeBPE [or (S ,S )-MeDuphos] have generally been described to give (S )- amino acids (ref. 19 and 20) as expected in the leucine part of celogentin C. In our synthesis, this diastereoselectivity outcome could not be yet confirmed; efforts to obtain a crystalline structure to confirm this diasteroselectivity were to date unsuccessful. Hopefully, we are expecting to get further information on this topic after the introduction of the left-handed peptidic part of celogentin C. By the way, in the presence of the (R ,R )-MeBPE ligand, a 16:84 dr was obtained illustrating the role of the remote tryptophan chiral center in the asymmetric hydrogenation.
