Martijn C. de Koning

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 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

An approach to the synthesis of peptide–PNA–peptide conjugates via native ligation

Abstract A convenient solid-phase synthesis of a PNA sequence containing an N-terminal thiaproline and a C-terminal thioester is described. The usefulness of this bifunctional PNA molecule is illustrated by the construction, based on native ligation, of a peptide–PNA–peptide adduct.

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.

Self‐Assembly Experiments with PNA‐Derivatized Carbon Nanotubes

We are conducting experiments to fabricate nanotube‐based field effect transistors (FETs) using the molecular recognition properties of DNA. For this purpose, we have prepared single‐walled carbon nanotubes derivatized with PNA (peptide nucleic acid, a DNA analog) and have studied their attachment to free, complementary DNA. We are currently examining the prospects for assembling devices by hybridization of the PNA‐labeled nanotubes to DNA‐functionalized electrodes.