Biosynthesis of the C_9–10unit of ajmaline and reserpine

Abstract

Glycine can be a specific precursor of the Cgvl0 unit (I) of ajmaline (11), and probably of reserpine (111), and may be a fundamental precursor for this unit in alkaloids.RECENTLY we reported that glycine could be specifically incorporated into the C,-,, unit as it occurs in the isoquinoline alkaloid cephaeline in Cephaelis acuminata, but that it was a poor precursor of fl-sitosterol in the same plant.lS2 At the same time it was confirmed that while acetic acid acts as a normal precursor of /%sitosterol, it is neither significantly nor specifically incorporated into cephaeline.2 We now present evidence that glycine is also specifically incorporated into this same C,,,, unit as it occurs in indole alkaloids found in RazLwoZfa seypentina, and hence that it may be a universal precursor of this unit.

Highly Selective Separation of Minimum‐Boiling Azeotrope Toluene/Pyridine by Nonporous Adaptive Crystals of Cucurbit[6]uril

“…The separation of this mixture faces a technical challenge owing to the formation of a minimum‐boiling azeotrope. Many methods can be used to separate azeotropic mixtures, for example, azeotropic distillation, pressure‐swing distillation, extractive distillation, adsorption, pervaporation using membranes, and some other new separation techniques . Specifically for toluene and pyridine, the present major technologies are pressure‐swing distillation, extractive distillation, and azeotropic distillation, performed in the presence of entrainers .…”

Highly Selective Separation of Minimum‐Boiling Azeotrope Toluene/Pyridine by Nonporous Adaptive Crystals of Cucurbit[6]uril

“…The separation of this mixture faces a technical challenge owing to the formation of a minimum-boiling azeotrope. Many methods can be used to separate azeotropic mixtures, for example, azeotropic distillation, [3] pressure-swing distillation, [4] extractive distillation, [5] adsorption, [6] pervaporation using membranes, [7] and some other new separation techniques. [8] Specifically for toluene and pyridine, the present major technologies are pressureswing distillation, extractive distillation, and azeotropic distillation, performed in the presence of entrainers.…”

“…We wondered whether cucurbit[n]urils crystals had the same behavior as NACs of macrocyclic arenes in addition to their permanently porous form. Herein, we, for the first time, utilized cucurbit- [6]uril (Q [6]) crystals as adsorptive separation materials to achieve the separation of the minimum-boiling azeotrope of toluene/pyridine (Scheme 1). We found that nonporous cucurbit [6]uril crystals (Q[6]a) separated pyridine from toluene with 100 % purity.…”

“…Herein, we, for the first time, utilized cucurbit- [6]uril (Q [6]) crystals as adsorptive separation materials to achieve the separation of the minimum-boiling azeotrope of toluene/pyridine (Scheme 1). We found that nonporous cucurbit [6]uril crystals (Q[6]a) separated pyridine from toluene with 100 % purity. The selectivity results from the formation of a host-guest complex between pyridine and Q [6], while toluene does not form a host-guest complex with Q [6] under these conditions.…”

“…We found that nonporous cucurbit [6]uril crystals (Q[6]a) separated pyridine from toluene with 100 % purity. The selectivity results from the formation of a host-guest complex between pyridine and Q [6], while toluene does not form a host-guest complex with Q [6] under these conditions. Furthermore, removal of pyridine from pyridine-loaded Q [6] leads to the pyridinefree cucurbit [6]uril structure, which can be recycled without losing performance.…”