Howard I. Duynstee

A convenient route to cis- and trans-fused bicyclic ethers by ruthenium mediated ring-closing metathesis of diene and enyne carbohydrate derivatives

Abstract A general approach towards the construction of highly functionalised pyranopyran and pyranofuran systems via Grubbs [Ru] catalysed ring-closing metatheses of neighbouring vinyl-O-allyl and vinyl-O-propargyl functions on monosaccharide scaffolds is described.

Synthesis of Verbascoside: A Dihydroxyphenylethyl Glycoside with Diverse Bioactivity

TMSOTf-mediated condensation of ethyl 4,6-O-benzylidene-1-thio-β-D-glucopyranoside (2) with peracetylated α-L-rhamnopyranosyl trichloroacetimidate donor 3a resulted in the formation of orthoester 4, which, after acetylation, rearranged into ethyl 3-O-(α-L-rhamnopyranosyl)-1-thio-β-D-glucopyranoside derivative 6a. The latter compound was converted into the corresponding trichloroacetimidate donors 8a–b. An alternative approach to trichloroacetimidate 8c commenced with the iodonium ion mediated glycosidation of ethyl 2,3,4-tri-O-benzoyl-1-thio-α-L-rhamnopyranside (15) with 1,2:5,6-diisopropylidene-D-glucofuranose (16) to afford disaccharide 17, which was transformed into 8c in five steps. Condensation of 8a–c with 2-[3,4-di-(tert-butyldimethyl-silyloxy)phenyl]ethanol (12) gave, after deacylation, key intermediate 14. Protecting-group manipulation of 14 and subsequent esterification of resulting 22 with 3,4-di-O-tert-butyldimethylsilylcaffeic acid (27) gave, after deprotection, verbascoside (1).

An Efficient Synthesis of (R)‐3‐{(R)‐3‐[2‐O‐(α‐L‐Rhamnopyranosyl)‐ α‐L‐rhamnopyranosyl] oxydecanoyl}oxydecanoic Acid, a Rhamnolipid from Pseudomonas Aeruginosa

N-iodosuccinimide/triflic acid mediated one-pot two-step glycosylation of ethyl 2,3,4-tri-O-benzyl-1-thio-α-L-rhamnopyranoside (8) with phenyl 3,4-O-(2,3-dimethoxybutane-2,3-diyl)-1-thio-α-L-rhamnopyranoside (10b) and phenacyl (R)-3-hydroxydecanoate (13) gave rhamnolipid 17. The latter was transformed in five steps into the title compound 2. Esterification of 2 with diazomethane resulted into the corresponding methyl ester derivative 1.

An expeditious route to the synthesis of kelampayosides A and B

Abstract Chemoselective NIS/ cat. TfOH-mediated glycosylation of ethyl2,3,4-tri-O-benzoyl-1-thio-β- d -glucopyranoside (13) with ethyl2,3-di-O-acetyl-5-O-benzyl-1-thio-αβ- d -erythro-apiofuranoside (4a) gave dimer14 in an excellent yield. BF3•Et2O-catalysed condensation of the α-trichloroacetimidate31, accessible in two steps from14, with 3,4,5-trimethoxyphenol gave β-linked derivative32 followed by deprotection gave Kelampayoside A. Protecting group manipulations of32 and subsequent caffeoylation of resulting36 followed by deprotection gave Kelampayoside B. Download : Download full-size image

Synthesis of Highly Functionalized Piperidines via a Tandem Retro‐Michael‐[2 + 3]‐Cycloaddition

The highly functionalized piperidine 5a was synthesized in only 4 steps starting from ribose using a tandem retro‐Michael‐[2 + 3]‐cycloaddition process as the key transformation. The versatility of the tandem retro‐Michael‐[2 + 3]‐cycloaddition was demonstrated by the synthesis of novel piperidines 5b, 5c, 11 and 16.

Synthesis of 3,4,5-trimethoxyphenyl 5″-O-caffeoyl-β-d-erythro-apiofuranosyl-(1→6)-β-d-glucopyranoside: Kelampayoside B

Chemoselective NIS/ cat. TfOH-mediated glycosylation of ethyl 2,3,4-tri-O-benzoyl-1-thio-β-d-glucopyranoside (4) with ethyl 2,3-di-O-acetyl-5-O-benzyl-1-thio-α/β-d-erythro-apiofuranoside (3) gave dimer 5 in an excellent yield. BF3Et2O-catalysed condensation of the α-trichloroacetimidate 18, accessible in two steps from 5, with 3,4,5-trimethoxyphenol gave β-linked derivative 19 which could be transformed in five steps into the title compound.