Reflections on a Copenhagen-Minneapolis Axis in Bioorganic Chemistry.

The international peptide community rejoiced when one of its most distinguished members, Morten Meldal of Denmark, shared the 2022 Nobel Prize in Chemistry. In fact, the regiospecific solid-phase "copper(I)-catalyzed 1,3-dipolar cycloaddition of terminal alkynes to azides" (CuACC) reaction-that formed the specific basis for Meldal's recognition-was reported first at the 17 American Peptide Symposium held in San Diego in June 2001. The present perspective outlines intertwining conceptual and experimental threads pursued concurrently in Copenhagen and Minneapolis, sometimes by the same individuals, that provided context for Meldal's breakthrough discovery.

Preparation, Characterization, and Mechanistic Considerations for 1,1,1-Tri(thioacetyl)ethane and 1,1-Di(thioacetyl)ethene.

Two new compounds, 1,1,1-tri(thioacetyl)ethane and 1,1-di(thioacetyl)ethene, arose during reactions of acetyl methoxy(thiocarbonyl) sulfide with potassium methyl xanthate. Relevant mechanisms were elucidated, which in turn suggested novel streamlined routes to these same compounds. Several further transformations of the title compounds were demonstrated, suggesting their potential synthetic utility.

Crystal structures of (N-methyl-N-phenyl-amino)(N-methyl-N-phenyl-carbamoyl)sulfide and the corresponding disulfane.

The title compounds, (N-methyl-N-phenyl-amino)(N-methyl-N-phenyl-car-bam-oyl)sulfide, C15H16N2OS, (I), and (N-methyl-N-phenyl-amino)-(N-methyl-N-phenyl-carbamo-yl)disulfane, C15H16N2OS2, (II), are stable derivatives of (chloro-carbon-yl)sulfenyl chloride and (chloro-carbon-yl)disulfanyl chloride, respectively. The torsion angle about the S-S bond in (II) is -92.62 (6)°, which is close to the theoretical value of 90°.

Crystal structure of O-ethyl N-(eth-oxy-carbon-yl)thio-carbamate.

The title compound, C6H11NO3S, provides entries to novel carbamoyl disulfanes and related compounds of inter-est to our laboratory. The atoms of the central O(C=S)N(C=O)O fragment have an r.m.

Crystal structures of three (trichloromethyl)(carbamoyl)disulfanes.

The present paper reports crystallographic studies on three related compounds that were of inter-est as precursors for synthetic and mechanistic work in organosulfur chemistry, as well as to model nitro-gen-protecting groups: (N-methyl-carbamo-yl)(tri-chloro-meth-yl)disulfane, C3H4Cl3NOS2, (1), (N-benzyl-carbamo-yl)(tri-chloro-meth-yl)disulfane, C9H8Cl3NOS2, (2), and (N-methyl-N-phenyl-carbamo-yl)(tri-chloro-meth-yl)disulfane, C9H8Cl3NOS2, (3). Their mol-ecular structures, with similar bond lengths and angles for the CCl3SS(C=O)N moieties, are confirmed. Compounds (1) and (3) both crystallized with two independent mol-ecules in the asymmetric unit.

Unexpectedly Stable (Chlorocarbonyl)(N-ethoxycarbonylcarbamoyl)disulfane, and Related Compounds That Model the Zumach-Weiss-Kühle (ZWK) Reaction for Synthesis of 1,2,4-Dithiazolidine-3,5-diones.

The Zumach-Weiss-Kühle (ZWK) reaction provides 1,2,4-dithiazolidine-3,5-diones [dithiasuccinoyl (Dts)-amines] by the rapid reaction of O-ethyl thiocarbamates plus (chlorocarbonyl)sulfenyl chloride, with ethyl chloride and hydrogen chloride being formed as coproducts, and carbamoyl chlorides or isocyanates generated as yield-diminishing byproducts. However, when the ZWK reaction is applied with (N-ethoxythiocarbonyl)urethane as the starting material, heterocyclization to the putative "Dts-urethane" does not occur. Instead, the reaction directly provides (chlorocarbonyl)(N-ethoxycarbonylcarbamoyl)disulfane, a reasonably stable crystalline compound; modified conditions stop at the (chlorocarbonyl)[1-ethoxy-(N-ethoxycarbonyl)formimidoyl]disulfane intermediate.

Crystal structure of bis-(N-methyl-N-phenyl-amino)-tris-ulfane.

The title compound, C14H16N2S3, crystallized with two independent mol-ecules [(1 a ) and (1 b )] in the asymmetric unit. Both mol-ecules display a pseudo-trans conformation. The two consecutive S-S bond lengths of the tris-ulfane unit of mol-ecule (1 a ) are 2.

The N-terminal zinc finger and flanking basic domains represent the minimal region of the human immunodeficiency virus type-1 nucleocapsid protein for targeting chaperone function.

The human immunodeficiency virus type-1 (HIV-1) nucleocapsid (NC) protein is a chaperone that facilitates nucleic acid conformational changes to produce the most thermodynamically stable arrangement. The critical role of NC in many steps of the viral life cycle makes it an attractive therapeutic target. The chaperone activity of NC depends on its nucleic acid aggregating ability, duplex destabilizing activity, and rapid on-off binding kinetics.

On the role of NMR spectroscopy for characterization of antimicrobial peptides.

Antimicrobial peptides (AMPs) provide a primordial source of immunity, conferring upon eukaryotic cells resistance against bacteria, protozoa, and viruses. Despite a few examples of anionic peptides, AMPs are usually relatively short positively charged polypeptides, consisting of a dozen to about a hundred amino acids, and exhibiting amphipathic character. Despite significant differences in their primary and secondary structures, all AMPs discovered to date share the ability to interact with cellular membranes, thereby affecting bilayer stability, disrupting membrane organization, and/or forming well-defined pores.

Synthesis and characterization of the 47-residue heterodimeric antimicrobial peptide distinctin, featuring directed disulfide bridge formation.

Distinctin, a 47-residue heterodimeric peptide with potent antimicrobial activity, comprises two monomeric units linked covalently by a disulfide bond between Cys19 from the 22-residue A chain and Cys23 from the 25-residue B chain. Previous synthetic strategies involved assemblies of the two individual chains, followed by their co-oxidation to form the connecting disulfide bridge, and resulted in a mixture of three species: two homodimers and one heterodimer. Here, we report synthesis of exclusively heterodimeric distinctin, using recently developed tactics for directed disulfide bridge formation.

Bis[(methyl-sulfan-yl)carbon-yl]disulfane.

The title compound, C(4)H(6)O(2)S(4), was prepared by repeating, with subtle improvements, a multi-step route originally described by Mott & Barany [J. Chem. Soc.

Bis(N-methyl-N-phenyl-carbamo-yl)disulfane.

The title compound, C(16)H(16)N(2)O(2)S(2), has been synthesized by several different high-yield routes, and has been encountered as a co-product in a number of reaction pathways, ever since it became of inter-est to our research program over 30 years ago. We now confirm the proposed mol-ecular structure in which the mol-ecule exhibits a twofold axis of symmetry through the mid-point of the S-S bond and the two planes defined by the (carbamo-yl)sulfenyl moieties are essentially perpendicular to each other [dihedral angle = 81.55 (14)°].

Deciphering structural elements of mucin glycoprotein recognition.

Mucin glycoproteins present a complex structural landscape arising from the multiplicity of glycosylation patterns afforded by their numerous serine and threonine glycosylation sites, often in clusters, and with variations in respective glycans. To explore the structural complexities in such glycoconjugates, we used NMR to systematically analyze the conformational effects of glycosylation density within a cluster of sites. This allows correlation with molecular recognition through analysis of interactions between these and other glycopeptides, with antibodies, lectins, and sera, using a glycopeptide microarray.

Synthetic routes to, transformations of, and rather surprising stabilities of (N-methyl-N-phenylcarbamoyl)sulfenyl chloride, ((N-methyl-N-phenylcarbamoyl)dithio)carbonyl chloride, and related compounds.

The title compound classes, (carbamoyl)sulfenyl chlorides and ((carbamoyl)dithio)carbonyl chlorides, have been implicated previously as unstable, albeit trappable, intermediates in organosulfur chemistry. The present work reports for each of these functional groups: (i) several routes to prepare it in the N-methylaniline family; (ii) its direct structural characterization by several spectroscopic techniques; (iii) its rather unexpected stability and its ultimate fate when it decomposes; (iv) a series of further chemical transformations that give highly stable derivatives, each in turn subject to thorough characterization. Relevant kinetic and mechanistic experiments were carried out, including some with p-methyl- and 2,6-dimethyl-substituted N-methylanilines.

Solid-phase synthesis and evaluation of glycopeptide fragments from rat epididymal cysteine-rich secretory protein-1 (Crisp-1).

Three 18-residue peptides with the sequence Glp-Asp-Thr-Thr-Asp-Glu-Trp-Asp-Arg-Asp-Leu-Glu-Asn-Leu-Ser-Thr-Thr-Lys, taken from the N-terminus of the rat epididymal cysteine-rich secretory protein (Crisp-1) that is important in the fertilization process, were prepared by Fmoc solid-phase synthesis using a convergent strategy. These peptides were the parent sequence, plus two possible α-O-linked T(N) antigen-containing glycopeptides with a Thr(α-D-GalNAc) residue in place of either Thr3 or Thr4. During chain assembly, two deletion peptides [des-Asp2 and des-Thr(Ac(3)-α-D-GalNAc)] and one terminated peptide [N-acetylated 14-mer] arose, as did several peptides in which aspartimide formation had occurred at each of the four possible positions in the sequence.

Intramolecular glycan-protein interactions in glycoproteins.

Glycoproteins are a major class of glycoconjugates displaying a variety of mutual interactions between glycan and protein moieties that ultimately affect molecular organization. Modulation of the pendant glycan structures is important in tuning the functions of glycoproteins. Here we discuss structural aspects and some of the challenges to studying intramolecular interactions between carbohydrate and protein elements in several forms of O-linked as well as N-linked glycoproteins.

On-resin conversion of Cys(Acm)-containing peptides to their corresponding Cys(Scm) congeners.

The Acm protecting group for the thiol functionality of cysteine is removed under conditions (Hg(2+)) that are orthogonal to the acidic milieu used for global deprotection in Fmoc-based solid-phase peptide synthesis. This use of a toxic heavy metal for deprotection has limited the usefulness of Acm in peptide synthesis. The Acm group may be converted to the Scm derivative that can then be used as a reactive intermediate for unsymmetrical disulfide formation.

Investigation of the sequence and length dependence for cell-penetrating prenylated peptides.

Cell penetrating peptides are useful delivery tools for introducing molecules of interest into cells. A new class of cell penetrating molecules has been recently reported-cell penetrating, prenylated peptides. In this study a series of such peptides was synthesized to examine the relationship between peptide sequence and level of peptide internalization and to probe their mechanism of internalization.

Structure and topology of monomeric phospholamban in lipid membranes determined by a hybrid solution and solid-state NMR approach.

Phospholamban (PLN) is an essential regulator of cardiac muscle contractility. The homopentameric assembly of PLN is the reservoir for active monomers that, upon deoligomerization form 1:1 complexes with the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA), thus modulating the rate of calcium uptake. In lipid bilayers and micelles, monomeric PLN exists in equilibrium between a bent (or resting) T state and a more dynamic (or active) R state.

Multifunctional prenylated peptides for live cell analysis.

Protein prenylation is a common post-translational modification present in eukaryotic cells. Many key proteins involved in signal transduction pathways are prenylated, and inhibition of prenylation can be useful as a therapeutic intervention. While significant progress has been made in understanding protein prenylation in vitro, we have been interested in studying this process in living cells, including the question of where prenylated molecules localize.

Effect of Mg(2+) and Na(+) on the nucleic acid chaperone activity of HIV-1 nucleocapsid protein: implications for reverse transcription.

The human immunodeficiency virus type 1 (HIV-1) nucleocapsid protein (NC) is an essential protein for retroviral replication. Among its numerous functions, NC is a nucleic acid (NA) chaperone protein that catalyzes NA rearrangements leading to the formation of thermodynamically more stable conformations. In vitro, NC chaperone activity is typically assayed under conditions of low or no Mg(2+), even though reverse transcription requires the presence of divalent cations.

HIV-1 nucleocapsid protein switches the pathway of transactivation response element RNA/DNA annealing from loop-loop "kissing" to "zipper".

The chaperone activity of HIV-1 (human immunodeficiency virus type 1) nucleocapsid protein (NC) facilitates multiple nucleic acid rearrangements that are critical for reverse transcription of the single-stranded RNA genome into double-stranded DNA. Annealing of the transactivation response element (TAR) RNA hairpin to a complementary TAR DNA hairpin is an essential step in the minus-strand transfer step of reverse transcription. Previously, we used truncated 27-nt mini-TAR RNA and DNA constructs to investigate this annealing reaction pathway in the presence and in the absence of HIV-1 NC.

Caged protein prenyltransferase substrates: tools for understanding protein prenylation.

Originally designed to block the prenylation of oncogenic Ras, inhibitors of protein farnesyltransferase currently in preclinical and clinical trials are showing efficacy in cancers with normal Ras. Blocking protein prenylation has also shown promise in the treatment of malaria, Chagas disease and progeria syndrome. A better understanding of the mechanism, targets and in vivo consequences of protein prenylation are needed to elucidate the mode of action of current PFTase (Protein Farnesyltransferase) inhibitors and to create more potent and selective compounds.

Disulfide bond formation in peptides.

The formation of disulfide bridges is often a crucial final stage in peptide synthesis. There is compelling evidence that the disulfide pattern can be critical in the folding and structural stabilization of many natural peptide and protein sequences, while the artificial introduction of disulfide bridges into natural or designed peptides may often improve biological activities/specificities and stabilities. This unit provides a highly selective, albeit state-of-the-art, menu of procedures that can be performed to establish intramolecular or intermolecular disulfide bridges in targets of varying complexities.