title: Anchor-linked intermediates in peptide amide synthesis are caused by dimeric anchors on the solid supports.
abstract: Cleavage and kinetic studies have been carried out using commercially obtained H-Tyr(tBu)-5-(4'-aminomethyl-3',5'-dimethoxyphenoxy)valeric acid-TentaGelS (H-Tyr(tBu)-4-ADPV-TentaGelS) and H-Tyr (tBu)-4-ADPV-Ala-aminomethyl-resin (H-Tyr(tBu)-4-ADPV-AM-resin) prepared from commercially available resin and loaded with commercially available Fmoc-4-ADPV-OH amide anchor. Cleavage with pure trifluoroacetic acid (TFA) gave the intermediate H-Tyr-4-ADPV-NH2, which was then degraded to H-Tyr-NH2, and cleavage with TFA/dichloromethane (1:9) yielded H-Tyr-4-ADPV-NH2 which could be isolated in preparative amounts. Cleavage reactions with 15N-labelled H-Ala-4-ADPV-(15N)-Gly-AM-resin yielded the intermediate H-Ala-4-ADPV-NH2, which contained no 15N as demonstrated by 1H-NMR. The analysis of the commercial Fmoc-4-ADPV-OH amide anchor showed the presence of Fmoc-4-ADPV-4-ADPV-OH as an impurity in high amounts. This dimeric anchor molecule is the cause of formation of the anchor-linked peptide intermediate obtained during the cleavage from the resin. The particularly high acid-lability of the amide bond between the two ADPV moieties was utilized to synthesize sidechain and C-terminally 4-ADPV protected pentagastrin on a double-anchor resin, and to cleave it using 5% trifluoroacetic acid in dichloromethane. This method may offer a new way for the synthesis of protected peptide amides with improved solubility to be used in fragment condensation.
authors.affiliation: Institut für Organische Chemie, Universität Tübingen, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Flechsler
authors.forename: A G
authors.initials: AG
authors.lastname: Beck-Sickinger
authors.forename: H
authors.initials: H
authors.lastname: Stephan
authors.forename: R
authors.initials: R
authors.lastname: Sheppard
authors.forename: G
authors.initials: G
authors.lastname: Jung
mesh_terms: D000577:Amides / Q000138:chemical synthesis / Q000737:chemistry; D000595:Amino Acid Sequence; D001665:Binding Sites; D019281:Dimerization; D005449:Fluorenes; D007202:Indicators and Reagents; D007700:Kinetics; D008722:Methods; D015394:Molecular Structure; D010418:Pentagastrin / Q000138:chemical synthesis / Q000737:chemistry; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry*; D012117:Resins, Synthetic; D012995:Solubility; D014631:Valerates
chemical_list: D000577:Amides; D005449:Fluorenes; D007202:Indicators and Reagents; D010455:Peptides; D012117:Resins, Synthetic; D014631:Valerates; C064395:5-(4-(9-fluorenylmethyloxycarbonyl)aminomethyl-3,5-dimethoxyphenoxy)valeric acid; D010418:Pentagastrin