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The polymyxin lipodecapeptides colistin and polymyxin B have become last resort therapies for infections caused by highly drug-resistant Gram-negative bacteria. Unfortunately, their utility is compromised by significant nephrotoxicity and polymyxin-resistant bacterial strains. We have conducted a systematic activity-toxicity investigation by varying eight of the nine polymyxin amino acid free side chains, preparing over 30 analogues using a novel solid-phase synthetic route. Compounds were tested against a panel of Gram-negative bacteria and counter-screened for in vitro cell toxicity. Promising compounds underwent additional testing against primary kidney cells isolated from human kidneys to better predict their nephrotoxic potential. Many of the new compounds possessed equal or better antimicrobial potency compared to polymyxin B, and some were less toxic than polymyxin B and colistin against mammalian HepG2 cells and human primary kidney cells. These initial structure-activity and structure-toxicity studies set the stage for further improvements to the polymyxin class of antibiotics.

The cytotoxic, cyclic heptadepsipeptide, natural product callipeltin B was synthesized on a solid-phase support in 15% overall yield. Comparison of the 1H NMR spectra of three synthetic isomers with those of callipeltin B confirmed the configurational reassignment of its threonine residues as d-allothreonine and the assignment of the configuration of its β-methoxytyrosine residue as (2R,3R). Copyright

A method is provided for the synthesis of glycopeptides using a sugar assisted ligation strategy, wherein an N-terminal peptide portion in the form of a thioester is coopled with a C-terminal peptide portion bearing a carbohydrate moiety comprising a thiol group.

The highly α-selective and scalable synthesis of the Fmoc-protected GalNAc-threonine amino acid and TN antigen in gram scale (0.5-1 g) is described. The challenging 1,2-cis-2-amino glycosidic bond is addressed through a coupling of threonine residues with C(2)-N-ortho-(trifluoromethyl)benzylidenamino trihaloacetimidate donors mediated by Ni(4-F-PhCN)4(OTf)2. The desired 1,2-cis-2-amino glycoside was obtained in 66% yield (3.77 g) with α-only selectivity and subsequently transformed into the Fmoc-protected GalNAc-threonine and TN antigen. This operationally simple procedure no longer requires utilization of the commonly used C(2)-azido donors and overcomes many of the limitations associated with the synthesis of 1,2-cis linkage.

The first solid-phase parallel synthesis of macrocyclic peptides using three-component coupling driven by aziridine aldehyde dimers is described. The method supports the synthesis of 9- to 18-membered aziridine-containing macrocycles, which are then functionalized by nucleophilic opening of the aziridine ring. This constitutes a robust approach for the rapid parallel synthesis of macrocyclic peptides. Solid-phase macrocycles: The first solid-phase parallel synthesis of macrocyclic peptides using three-component coupling driven by aziridine aldehyde dimers is described. The method supports the synthesis of 9- to 18-membered aziridine-containing macrocycles, which are then functionalised by nucleophilic opening of the aziridine ring (see scheme). This constitutes a robust approach for the rapid parallel synthesis of macrocyclic peptides.

Antifreeze glycoproteins (AFGPs) are glycosylated polypeptides produced by Antarctic and Arctic fishes, which allow them to survive in seawater at sub-zero temperatures. An investigation into the postulated enteric uptake of AFGP synthesized in the exocrine pancreas of Antarctic fishes required a custom-prepared AFGP probe that incorporated seven isotopically-labelled Ala residues for detection by mass spectrometry. The AFGPs are composed of a repetitive three amino acid unit (Ala-Ala-Thr), in which the threonine residue is glycosylated with the disaccharide β-d-Gal-(1→3) α-d-GalNAc. The synthesis of isotopically-labelled AFGP8 (1), as well as the optimized synthesis of the protected glycosylated amino acid building block 2, is reported.

Photolabile caging groups, including the 1-(2-nitrophenyl)ethyl (NPE) group, have been applied to probe many biological processes, including protein phosphorylation. Although studies with NPE-caged phosphoamino acids have provided valuable information, these investigations have been limited to the use of only one caged species in a single experiment. To expand the scope of these tools, we have developed an approach for sequentially uncaging two different phosphopeptides in one system, enabling interrogation of multiple phosphorylation events. We present the synthesis of [7-(diethylamino)coumarin-4- yl]methyl (DEACM)-caged phosphorylated serine, threonine, and tyrosine building blocks for Fmoc-based solid-phase peptide synthesis to allow convenient incorporation of these residues into peptides and proteins. Exposure of DEACM- and NPE-caged phosphopeptides to 420 nm light selectively releases the DEACM group without affecting the NPE-caged peptide. This then enables a subsequent irradiation event at 365 nm to remove the NPE group and liberate a second phosphopeptide. We demonstrate the versatility of this general sequential uncaging approach by applying it to control Wip1 phosphatase with two wavelengths of light.

The first straightforward building block based (non-interassembly) synthesis of peptides containing adenylylated serine and threonine residues is described. Key features include final global acidolytic protective group removal as well as full compatibility with standard Fmoc solid-phase peptide synthesis (SPPS). The described Thr-AMP SPPS-building block has been employed in the synthesis of the Thr-adenylylated sequence of human GTPase CDC42 (Ac-SEYVP-T(AMP)-VFDNYGC-NH2). Further, we demonstrate proof-of-concept for the synthesis of an Ser-adenylylated peptide (Ac-GSGA-S(AMP)-AGSGC-NH2) from the corresponding adenylylated serine building block.

The immobilization of alcohols onto 2-chlorotritylchloride resin using microwave irradiation was studied. Three different Fmoc-aminoalcohols were tested: the phenol-like Fmoc-tyramine, the primary alcohol Fmoc-ethanolamine, and the secondary alcohol Fmoc-

Fluorescently labelled glycopeptides containing GalNAcα1-O-Ser/Thr residues provide valuable immunological probes for the development of cancer vaccines. The microwave-assisted automated Fmoc solid-phase synthesis of a series of 5(6)-carboxyfluorescein-labelled GalNAcα1-O-Ser/Thr peptides is described. Lys(Dde)-Gly-Wang polystyrene resin was elongated using Fmoc SPPS with incorporation of several GalNAcα1-O-Ser/Thr residues. Deprotection of the Lys(Dde) then allowed attachment of the 5(6)-carboxyfluorescein label. The synthetic methodology described is flexible and suitably robust enabling the incorporation of three contiguous GalNAcα1-O-Ser residues into the peptide chain. Georg Thieme Verlag Stuttgart · New York.

An efficient new strategy for the synthesis of peptide and glycopeptide thioesters is described. The method relies on the side-chain immobilization of a variety of Fmoc-amino acids, protected at their C-termini, on solid supports. Once anchored, peptides were constructed using solid-phase peptide synthesis according to the Fmoc protocol. After unmasking the C-terminal carboxylate, either thiols or amino acid thioesters were coupled to afford, after cleavage, peptide and glycopeptide thioesters in high yields. Using this method a significant proportion of the proteinogenic amino acids could be incorporated as C-terminal amino acid residues, therefore providing access to a large number of potential targets that can serve as acyl donors in subsequent ligation reactions. The utility of this methodology was exemplified in the synthesis of a 28 amino acid glycopeptide thioester, which was further elaborated to an N-terminal fragment of the glycoprotein erythropoietin (EPO) by native chemical ligation.

Sugar-assisted ligation (SAL) presents an attractive strategy for the synthesis of glycopeptides, including the synthesis of cysteine-free β-O-linked and N-linked glycopeptides. Here we extended the utility of SAL for the synthesis of α-O-linked glycopeptides and glycoproteins. In order to explore SAL in the context of glycoprotein synthesis, we developed a new chemical synthetic route for the α-O-linked glycoprotein diptericin ε. In the first stage of our synthesis, diptericin segment Cys(Acm) 37-Gly52 and segment Val53-Phe82 were assembled by SAL through a Gly-Val ligation junction. Subsequently, after Acm deprotection, diptericin segment Cys37-Phe82 was ligated to segment Asp1-Asn36 by means of native chemical ligation (NCL) to give the full sequence of diptericin ε. In the final synthetic step, hydrogenolysis was applied to remove the thiol handle from the sugar moiety with the concomitant conversion of mutated Cys37 into the native alanine residue. In addition, we extended the applicability of SAL to the synthesis of glycopeptides containing cysteine residues by carrying out selective desulfurization of the sulfhydryl-modified sugar moiety in the presence of acetamidomethyl (Acm) protected cysteine residues. The results presented here demonstrated for the first time that SAL could be a general and useful tool in the chemical synthesis of glycoproteins.

Oxytocin structure was modified in position 4 using glycoamino acids. Procedure for transformation of Fmoc-protected serine and threonine derivatives into appropriate O-glycosylated precursors suitable for solid phase peptide synthesis (SPPS) was worked o

The Tn, T, sialyl-Tn, and 2,3-sialyl-T antigens are tumor-associated carbohydrate antigens expressed on mucins in epithelial cancers, such as those affecting the breast, ovary, stomach, and colon. Glycopeptides carrying these antigens are of interestfor development of cancer vaccines and a short, chemoenzymatic strategy for their synthesis is reported. Building blocks corresponding to the Tn (Ga1NAcα-Ser/Thr) and T [Galβ(1→3)Ga1NAcα-Ser/Thr] antigens, which are relatively easy to obtain by chemical synthesis, were prepared and then used in the synthesis of glycopeptides on the solid phase. Introduction of sialic acid to give the sialyl-Tn [Neu5Acα(2→6)Ga1NAcα-Ser/Thr] and 2,3-sialyl-T [Neu5Acα(2→3)Ga1β(1→3)Ga1NAcα-Ser/ Thr] antigens is difficult when performed chemically at the building block level. Sialylation was therefore carried out with recombinant sialyltransferases in solution after cleavage of the Tn and T glycopeptides from the solid phase. In the same manner, the core 2 trisaccharide [Ga1β1→3(G1cNAcβ1→6)Ga1NAc] was incorporated in glycopeptides containing the T antigen by using a recombinant N-acetylglucosaminyltransferase. The outlined chemoenzymatic approach was applied to glycopeptides from the tandem repeat domain of the mucin MUCl, as well as to neoglycosylated derivatives of a T cell stimulating viral peptide.

The building blocks O1-(2,3,4,6-tetra-O-acetyl-β-D- galactopyranosyl)-Nα(fluoren-9-ylmethoxycarbonyl)serine (5)and O 1-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl) -Nα-(fluoren-9-ylmethoxycarbonyl)threonine (6) for use in solid-phase glycopeptide synthesis can be obtained via their ally esters by mild treatment with tetrakis(triphenylphosphine)palladium(0) and tributyltin hydride with no Fmoc elimination or sugar cleavage or anomerization.