A Convenient Protocol for Selective Cleavage of 2-Hydroxy Acid Amides. Application to Semisynthesis of the Cyclic Heptapeptide Aza HUN-7293
摘要:
A two-step protocol for the first chemoselective cleavage of 2-hydroxy acid amides has been developed. Mesylation of the model substrate 2-(hydroxypropionylamino)-4-methylpentanoic acid methyl ester (11) followed by treatment with N-ethylthiourea (13) allows cleavage of 2-hydroxy acid amides under smooth conditions. Successful application of this methodology to the open-chain transesterification product 15 (methylester) of the cyclic heptadepsipeptide HUN-7293, a potent inhibitor of inducible cell adhesion molecule expression, delivered the corresponding hexapeptide 18 with unprotected N-terminus in 70-75% yield. This result demonstrates that the protocol developed even works in the presence of an ester and several methylated and unmethylated amide bonds. Finally, a sequence of ligation of methyl D-dehydroglutaminate (20) to the C-terminus of the saponification product 21, followed by the degradation protocol and ring closure, allowed chemical "point mutation" at the DGCN site affording the aza analogue of HUN-7293 (24) in 15% overall yield. To the best of our knowledge this is the first report on chemoselective cleavage of 2-hydroxy acid amides.
Optically pure (R)-(+)-lithium lactate (7) and its benzyl ether analogue (6a) were obtained from acetaldehyde using Eliel's 1,3-trans-oxathiane (1) as the chiral auxiliary for chromatographic separation.
Stereochemical Requirements for β-Hairpin Formation: Model Studies with Four-Residue Peptides and Depsipeptides
作者:Tasir S. Haque、Jennifer C. Little、Samuel H. Gellman
DOI:10.1021/ja960429j
日期:1996.1.1
associated with β-hairpins containing a two-residue loop between the strand segments. Each of our four-residue molecules containsproline at the second position, to promote a central β-turn. The β-turn is induced to be either “common” or “mirror-image”, relative to the outer residues, by choice of residue configuration (l vs d). In methylene chloride, end-capped tetrapeptide Ac−l-Val-d-Pro-d-Ala-l-Leu-NMe2
Synthesis of cell-wall analogues of vancomycin-resistant enterococci using solid phase peptide synthesis
作者:Younghoon R. Cho、Richard M.H. Entress、Dudley H. Williams
DOI:10.1016/s0040-4039(97)01110-6
日期:1997.7
A convenient method for the direct coupling of lithium d-lactate to 2-chlorotrityl chloride resin enabled the rapid and efficient solid phase synthesis of bacterialcell-wallprecursor analogues (depsipeptides) found in vancomycin-resistant enterococci (VRE).
A platinum(II) terpyridine complex having an enantiopure lactate anion afforded hydrated crystals l- or d-1hyd containing infinite chains of interacting Pt centers, while their dehydration induced crystal-to-crystal transformation into l- or d-1dehyd, respectively, exhibiting less significant Pt–Pt and/or ligand–ligand interactions. That transformation was accompanied by changes in the color as well
Synthesis of Haptenic Trimers Corresponding to the Cell Wall Glycopeptidolipids of<i>Mycobacterium Avium</i>Serovar 12
作者:Korien Zegelaar-Jaarsveld、Simon C. van der Plas、Gijs A. van der Marel、Jacques H. van Boom
DOI:10.1080/07328309608005677
日期:1996.7
The preparation of the spacer-containing trimers 2, 3-aminopropyl 3-O-[4-O-Me-3-O-(4-N-D,L-lactoyl-3-O-Me-beta-D-Quip)-alpha-L-Rhap]-alpha-L-Rhap, derivatives of the antigenic determinant of the glycopeptidolipid from Mycobacterium avium serotype 12, are described. Thus, iodonium ion-mediated glycosylation of the spacer-containing acceptor 7 with ethyl 1-thio-rhamnopyranoside donor 10, followed try selective deprotection of the p-methoxybenzyl group of thus obtained 19 gave bis-rhamnopyranoside acceptor 20. Elongation of 20 with ethyl 4-azido-1-thio-beta-D-quinovopyranoside 18 and subsequent reduction of the azido function in 21 led to trimer 22. The amino group in 22 was coupled with both D- and L-lactic acid to give, after removal of the protective groups, trimers 2.
High Affinity Surface Binding of a Strongly Dimerizing Vancomycin-Group Antibiotic to a Model of Resistant Bacteria
作者:Dominic P. O'Brien、Richard M. H. Entress、Matthew A. Cooper、Simon W. O'Brien、Andrew Hopkinson、Dudley H. Williams
DOI:10.1021/ja9839769
日期:1999.6.1
The factors that give rise to binding enhancements when a strongly dimerizing vancomycin-group antibiotic (chloroeremomycin) binds to a model cell surface of vancomycin-resistant enterococci (VRE) have been semiquantitated. The model cell surface is comprised of vesicles to which have been anchored cell wall precursor analogues of vancomycin-resistant bacteria (which terminate in -D-lactate) via a hydrophobic docosanoyl (C-22) chain. Using H-1 and F-19 NMR spectroscopy, a large binding enhancement at the model cell surface (compared to the binding of an analogous ligand in free solution) has been observed. This enhancement can be partitioned into two distinct factors: a simple concentrating factor arising from an-increase in local concentration of ligand when it is located at the vesicle surface and a factor arising from the cooperative interaction of species mutually bound to the membrane surface. The overall enhancement to binding at a surface compared to binding in free solution was found to be a factor of 10(2)-10(3). In contrast, no significant surface binding enhancement was observed for the weakly dimerizing antibiotic vancomycin.