Macroline/sarpagine-related oxindole

Table 5 Macroline/sarpagine-related oxindole alkaloids...

The partial synthesis70 of macroline (136) from normacusine B (140) was inspired by its postulated biosynthesis from a sarpagine-type precursor. Normacusine B (140), prepared by a previously published route from perivine, was protected at the primary alcohol group and then methylated on Na. Direct epoxidation of the product (141) failed however, osmylation gave the desired diol together with the related oxindole obtained by simultaneous oxidation of the indole double-bond, followed by rearrangement. Conversion of these diols into the related epoxides gave a mixture of (142) and (143), from which the desired epoxide (142) could be separated satisfactorily by fractional crystallization. 

Illustrated in Tables 2—6 are the structures of the recently isolated (since year 2000) sarpagine-related indole alkaloids, along with their key physicochemical properties. They have been classified into sarpagine-type, macroline-type, ajmaline-type, sarpagine/macroline oxindoles, and bisindole alkaloids containing sarpagine/macroHne monomeric units for ease of illustration. 

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