Encore, Encore!
Two hot areas of research served up second helpings online this week:
Synthesis Machines: Over at Nature, Kobayashi published a flow reactor approach to syntheses of either enantiomer of rolipram, an anti-inflammatory. No MIDA-boronate 'handles' here; this is classic chemistry - olefination, 1,4 addition, reduction, hydrolysis, decarboxylation, cyclization - performed over heterogeneous catalyst beds encased in stainless steel tubes. The group spices up the synthesis by including their in-house chiral PyBOX-calcium catalyst to control the 1,4 addition, and developing a Pd / polysilane-catalyzed reduction for a troublesome nitro group.
C-H Azidation: Remember John Hartwig's iron-meets hypervalent iodide combination from last March? It possessed the power to insert a late-stage amine equivalent into complex natural products. John Groves has raised the stakes, disclosing a "practical and complementary" Mn-porphyrin promoted version that takes solid sodium azide as the precursor.
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| Source: Groves, JACS ASAP |
The group finds it can enable late-stage azidation of a variety of complex bioactive substances (sclareolide, artemisinin, estrone, papaverine). Even more surprisingly, although likely a radical-induced transformation, using a chiral salen led to a single example of 70% ee material. Groves admits they have work to do, but the fact that this reaction operates with 1% loading in wet ethyl acetate at room temperature sure sounds promising!
Kobayashi claims his synthetic engine can produce a gram of 96% ee material every 24 hours, and that the system remains stable and operable for about a week's time. In a complementary Commentary, Joel Hawkins of Pfizer presents a tantalizing future, where hood-sized continuous synthesis units chug through kilo quantities of drug precursors, using commercial reagents, sans column chromatography.
