Chelation as a Driving Force in Organic Reactions. IV.¹ Synthesis of α-Nitro Acids by Control of the Carboxylation-Decarboxylation Equilibrium²

2-nitro-3-(p-hydroxyphenyl)propionate and aci-1-nitro-2-(p-hydroxyphenyl)ethane, two intermediates in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench.

“…a-Nitrosocarboxylates decarboxylate to oximes. a-Nitrocarboxylates are labile in aqueous solutions at physiological pH and decarboxylate to aci-nitro compounds (18,19). According to this reaction, the aci-tautomer of the nitro compound is the enzymatically active species.…”

“…The equilibrium favors the nitro compound (19,20), and the observed accumulation of the nitro compound with N-hydroxytyrosine as a substrate may reflect tautomerization of the aci-nitro compound released from the active site on the microsomal enzyme system. The involvement of the aci-nitro compound as the enzymatically active species would explain the low metabolic activity observed upon administration of the parent nitro compound (12).…”

The Biotin‐Dependent Enzymes

“…I n contrast, bicarbonate because of resonance stabilization is apparently less prone to nucleophilic attack and, therefore, might be expected to require enzyme-mediated electrophilic activation. Precedent for the electrophilic activation of bicarbonate has been obtained with magnesium methyl carbonate, an analogue of bicarbonate (301)(302)(303)(304)(305)(306). Stiles (301,302) has demonstrated that this reagent acts as an electrophilic carboxylating species in reactions with ketones which contain enolizable methyl or methylene groups.…”

Design, synthesis, and anti-inflammatory activity both in vitro and in vivo of new betulinic acid analogues having an enone functionality in ring A

“…Methyl ester 21 was prepared in 85% yield from methyl betulonate (20), which was easily synthesized in 95% yield in 2 steps (methylation with CH 2 N 2 and Jones oxidation) from 1, by Stiles' reagent (methoxymagnesium methyl carbonate) in DMF, 15 followed by methylation with CH 2 N 2 . The 1 H NMR spectrum showed that 21 is the single tautomer in CDCl 3 as depicted in Scheme 2.…”