A novel and efficient procedure for the preparation of allylic alcohols from α,β-unsaturated carboxylic esters using LiAlH4/BnCl

Anaerobic demethylation of guaiacyl-derived monolignols enabled by a designed artificial cobalamin methyltransferase fusion enzyme

Lignin-derived aryl methyl ethers (e.g. coniferyl alcohol, ferulic acid) are expected to be a future carbon source for chemistry. The well-known P450 dependent biocatalytic O-demethylation of these aryl methyl ethers is prone to side product formation especially for the oxidation sensitive catechol products which get easily oxidized in the presence of O₂. Alternatively, biocatalytic demethylation using cobalamin dependent enzymes may be used under anaerobic conditions, whereby two proteins, namely a methyltransferase and a carrier protein are required. To make this approach applicable for preparative transformations, fusion proteins were designed connecting the cobalamin-dependent methyltransferase (MT) with the corrinoid-binding protein (CP) from Desulfitobacterium hafniense by variable glycine linkers. From the proteins created, the fusion enzyme MT-L5-CP with the shortest linker performed best of all fusion enzymes investigated showing comparable and, in some aspects, even better performance than the separated proteins. The fusion enzymes provided several advantages like that the cobalamin cofactor loading step required originally for the CP could be skipped enabling a significantly simpler protocol. Consequently, the biocatalytic demethylation was performed using Schlenk conditions allowing the O-demethylation e.g. of the monolignol coniferyl alcohol on a 25 mL scale leading to 75% conversion. The fusion enzyme represents a promising starting point to be evolved for alternative demethylation reactions to diversify natural products and to valorize lignin.

First total syntheses of two natural glycosides

Isosyringinoside (1) and 3-(O-β-_d-glucopyranosyl)-α-(O-β-_d-glucopyranosyl)-4-hydroxy phenylethanol (2), the natural bioactive compounds contained unique structures, were first totally synthesized using easily available materials in short convenient routes with overall yields of 20.2% and 27.0%, respectively. An efficient total synthesis of 1 was developed in six steps, which contained two key steps of highly regioselective glycosylation without any selective protection steps. The seven-step synthesis of 2 involved two steps of regioselective glycosylations using BF₃-O(C₂H₅)₂ and TMSOTf as catalysts, respectively.

Facile Chemoselective Strategy toward Capturing Sphingoid Bases by a Unique Glutaraldehyde-Functionalized Resin

Sphingoid bases, which have a 2-amino-1,3-diol common functional group, are the structural backbone units of all sphingolipids. Recently, much attention has been focused on sphingoid bases because of their potentially beneficial bioactivities toward various cancer cells as well as their dietary interest. However, low abundance and the handling complexity caused by their amphiphilic character led to very limited research on them. Glutaraldehyde has two aldehyde groups, and it reacts rapidly with the 2-amino-1,3-diol functional group of sphingosine to give a tricyclic product. Immobilization of glutaraldehyde on a resin was successfully performed by organic synthesis, starting from trans-p-coumaric acid via eight steps. This approach suppresses the self-polymerization of glutaraldehyde, and addition of water to the developed resin causes the formation of cyclic double hemiacetal function, which avoids oxidation like a reducing sugar in nature and makes it stable even for up to 1 year incubation. The resin was applied to the solid-phase extracting experiment of free sphingosine from human serum at a concentration of 280 nM. Another extraction study of edible golden oyster mushrooms showed that the sphingoid base was selectively captured from complex natural extracts. These results demonstrate that the developed glutaraldehyde resin method is a highly selective method, and hence, the combination of it with the o-phthaldialdehyde HPLC method was confirmed as an efficient and sensitive method for analysis of sphingoid bases in biological samples.

HM, Nair VA. Anti selective glycolate aldol reactions of (S)-4-isopropyl-1-[(R)-1-phenylethyl]imidazolidin-2-one: application towards the asymmetric synthesis of 8-4′-oxyneolignans

The anti selective glycolate aldol reactions of (S)-4-isopropyl-1-[(R)-1-phenylethyl]imidazolidin-2-one auxiliary have been standardized with high yields and excellent diastereoselectivities on various substituted aryl, allyl and alkyl aldehydes.

Catalytic conversion of glycerol to allyl alcohol; effect of a sacrificial reductant on the product yield

Significant enhancement on the yield of the allyl alcohol is obtained where a reductant is added to the glycerol feed.