Putative uniflorines

Next, Pyne et al. successfully utilized the synthetic methodology created for putative uniflorine 75 to construct the analogous castanospermine (84, Scheme 2.19) [38]. In this case, amino-tetraol 81 had to be protected with three different protecting groups resulting in compound 82. Treatment of 82 with [Ru]-II (10mol%) yielded pyrrolo-oxazolone 83 in 88% yield. Diastereoselective syn-dihydroxylation of the olefin, followed by several steps, led then to castanospermine (84). 

Enantioenriched 196 was prepared by ring rearrangement metathesis (RRM) of 197. Through the agency of regio- and stereo-controlled hydroxylation reactions, (+)-castanospermine 198 and both isomers 199 of the pentahydroxylated indolizidine uniflorine-A of putative structure 200 were prepared as shown in Scheme 57 <05T8888>. 

Scheme 2.17 Retrosyntheses of (+)-lentiginosine (74) and the putative structure of uniflorine A (75) proceed via similar RCM precursors (76 for 74, 77 for 75).

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