Determination of chemical shifts in 6-condensed syringylic lignin model compounds

A small library of 6-substituted syringyl model compounds with aliphatic, carboxylic, phenylic, benzylic alcohols and brominated substituents were prepared. The influence of the substituents on the chemical shifts of the compounds was analyzed. All of model compounds showed a characteristic increase in the 13C NMR chemical shift of the methoxy group vicinal to the substitution. This 13C NMR peak and its corresponding correlation peak in HSQC could potentially be used to identify 6-condensation in syringylic lignin samples.

Pseudo High-Throughput Development and Optimization of the Electrochemical Oxidation of Sensitive Propargylic Benzylic Alco-hols

The electrochemical oxidation of sensitive propargylic benzylic alcohols having varying substituents is reported. The ther-mal oxidation of propargylic benzylic alcohols presents an acute challenge in the synthesis of complex molecules and various traditional oxidation methods proceed with low efficiency or not at all. We describe the convenient preparation and charac-terization of N-hydroxytetrafluorophthalimide (TFNHPI) and a practical, green electrochemical oxidation protocol that em-ploys TFNHPI as a stable, efficient electrochemical mediator. The electrochemical method employing TFNHPI to oxidize propargylic benzylic alcohols was developed and optimized in pseudo high-throughput fashion using a bank of inexpensive two-electrode power supplies. The electrochemical oxidation of propargylic benzylic alcohol was also leveraged to develop efficient synthetic pathways to prepare gram quantities of resveratrol natural products such as the pauciflorols.

Chemoenzymatic One-Pot Process for the Synthesis of Tetrahydroisoquinolines

1,2,3,4-Tetrahydyroisoquinolines form a valuable scaffold for a variety of bioactive secondary metabolites and commercial pharmaceuticals. Due to the harsh or complex conditions of the conventional chemical synthesis of this molecular motif, alternative mild reaction pathways are in demand. Here we present an easy-to-operate chemoenzymatic one-pot process for the synthesis of tetrahydroisoquinolines starting from benzylic alcohols and an amino alcohol. We initially demonstrate the oxidation of 12 benzylic alcohols by a laccase/TEMPO system to the corresponding aldehydes, which are subsequently integrated in a phosphate salt mediated Pictet–Spengler reaction with m-tyramine. The reaction conditions of both individual reactions were analyzed separately, adapted to each other, and a straightforward one-pot process was developed. This enables the production of 12 1,2,3,4-tetrahydyroisoquinolines with yields of up to 87% with constant reaction conditions in phosphate buffer and common laboratory glass bottles without the supplementation of any additives.