CD Spectroscopic Methods Research Articles

Thermodynamic and structural characterization of the macrochelates formed in the reactions of copper(II) and zinc(II) ions with peptides of histidine

Copper(II) complexes of the peptides Ac-HisSarHis-NH 2, Ac-HisSarHisSarHis-NH 2 and Ac-HisSarHisSarHisSarHis-NH 2 have been studied by potentiometric, UV–Vis, CD and EPR spectroscopic methods. Stability constants for the corresponding zinc(II) complexes have also been reported. The formation of M(II)–2N im, M(II)–3N im and M(II)–4N im bonded macrochelates was suggested in the pH range 5–7. The macrochelates were, however, not stable enough to prevent metal ion hydrolysis in slightly alkaline solutions. In the case of copper(II) complexes, the metal ion promoted deprotonation and coordination of the amide groups of histidyl residues were also suggested. The stability constants of macrochelate complexes were compared to the literature data reported for the macrochelates of the other peptides of histidine. It was found that the thermodynamic stability of macrochelate species is largely influenced by the number and location of histidyl residues in the peptide backbone. The highest stability was obtained for the HXHYH-type sequences, while the distant arrangement of histidyl residues resulted in a significant reduction of the stability constants.

Polyamine Analogues Bind Human Serum Albumin

Polyamine analogues show antitumor activity in experimental models, and their ability to alter activity of cytotoxic chemotherapeutic agents in breast cancer is well documented. Association of polyamines with nucleic acids and protein is included in their mechanism of action. The aim of this study was to examine the interaction of human serum albumin (HSA) with several polyamine analogues, such as 1,11-diamino-4,8-diazaundecane (333), 3,7,11,15-tetrazaheptadecane.4HCl (BE-333), and 3,7,11,15,19-pentazahenicosane.5HCl (BE-3333), in aqueous solution at physiological conditions using a constant protein concentration and various polyamine contents (microM to mM). FTIR, UV-visible, and CD spectroscopic methods were used to determine the polyamine binding mode and the effects of polyamine complexation on protein stability and secondary structure. Structural analysis showed that polyamines bind nonspecifically (H-bonding) via polypeptide polar groups with binding constants of K333 = 9.30 x 10(3) M(-1), KBE-333 = 5.63 x 10(2) M(-1), and KBE-3333 = 3.66 x 10(2) M(-1). The protein secondary structure showed major alterations with a reduction of alpha-helix from 55% (free protein) to 43-50% and an increase of beta-sheet from 17% (free protein) to 29-36% in the 333, BE-333, and BE-3333 complexes, indicating partial protein unfolding upon polyamine interaction. HSA structure was less perturbed by polyamine analogues compared to those of the biogenic polyamines.

Contrasting Impact of DNA Repair GeneXRCC1PolymorphismsArg399GlnAndArg194Trpon The Risk of Lung Cancer in the North-Indian Population

DNA-RNase H adducts were used for site specific cleavage of RNA and DNA-RNA duplexes, whereas nonspecific DNA interaction with ribonuclease A (RNase A) has been observed. The aim of this study was to examine the complexation of calf-thymus DNA with RNase A at physiological condition, using constant DNA concentration (12.5 mM) and various protein contents (1 microM to 270 microM). FTIR, UV-visible, and CD spectroscopic methods were used to analyse protein binding mode, the binding constant and the effects of nucleic acid-enzyme interaction on both DNA and protein conformations. Our structural analysis showed a strong RNase-PO2 binding and minor interaction with G-C bases with overall binding constant of K = 6.1 x 10(4) M(-1). The RNase-DNA interaction alters the protein secondary structure with a major reduction of the alpha-helix and increase of the beta-sheet and random structure, while DNA remains in the B-family structure.

Chiral Polyfluorene Derivatives: Synthesis, Chiroptical Properties, and Investigation of the Structure−Property Relationships

Four polyfluorene derivatives with chiral center in the backbone or at the side chain, PLPheF (P1), PLPhGlyF (P2), PDPheF (P3), and PSPF (P4), have been designed and synthesized through the Pd-catalyzed Suzuki polymerization. The structures of these polymers are characterized by 1H and 13C NMR, UV−vis, photoluminescence (PL), and CD spectroscopic methods as well as elemental analysis. These four polymers exhibit the linearly polarized photoluminescence in dilute solutions. The investigation of the absorption and emission behaviors indicates that the aggregates and/or the excited states excimers might be formed in THF solution at higher concentrations. We also observe the emission dichroic ratio RPL of these polymers in films is increased in comparison with that in solutions. After film annealing, polymers P1, P2, and P3 also show obvious linearly polarized photoluminescence at 500−650 nm. Moreover, the films of polymer P4 exhibit good thermal spectral stability after annealing in comparison with other thr...

Resveratrol Binding to Human Serum Albumin

Resveratrol (Res), a polyphenolic compound found largely in the skin of red grape and wine, exhibits a wide range of pharmaceutical properties and plays a role in prevention of human cardiovascular diseases [Pendurthi et al., Arterioscler. Thromb. Vasc. Biol. 19, 419–426 (1999)]. It shows a strong affinity towards protein binding and used as inhibitor for cyclo- oxygenase and ribonuclease reductase. The aim of this study was to examine the interaction of resveratrol with human serum albumin (HSA) in aqueous solution at physiological conditions, using a constant protein concentration (0.3 mM) and various pigment contents μM to mM). FTIR, UV-Visible, CD, and fluorescence spectroscopic methods were used to determine the resveratrol binding mode, the binding constant and the effects of pigment complexation on protein secondary structure. Structural analysis showed that resveratrol bind non-specifically (H-bonding) via polypeptide polar groups with overall binding constant of KRes = 2.56× 105 M−1. The protein secondary structure, analysed by CD spectroscopy, showed no major alterations at low resveratrol concentrations (0.125 mM), whereas at high pigment content (1 mM), major increase of α-helix from 57% (free HSA) to 62% and a decrease of β-sheet from 10% (free HSA) to 7% occurred in the resveratrol-HSA complexes. The results indicate a partial stabilization of protein secondary structure at high resveratrol content.

Retinol and retinoic acid bind human serum albumin: Stability and structural features

Vitamin A components, retinol and retinoic acid, are fat-soluble micronutrients and critical for many biological processes, including vision, reproduction, growth, and regulation of cell proliferation and differentiation. The cellular uptake of Vitamin A is through specific interaction of a plasma membrane receptor with serum retinol-binding protein. Human serum albumin (HSA), as a transport protein, is the major target of several micronutrients in vivo. The aim of present study was to examine the interaction of retinol and retinoic acid with human serum albumin in aqueous solution at physiological conditions using constant protein concentration and various retinoid contents. FTIR, UV–vis, CD and fluorescence spectroscopic methods were used to determine retinoid binding mode, the binding constant and the effects of complexation on protein secondary structure. Structural analysis showed that retinol and retinoic acid bind non-specifically (H-bonding) via protein polar groups with binding constants of K ret = 1.32 (±0.30) × 10 5 M −1 and K retac = 3.33 (±0.35) × 10 5 M −1. The protein secondary structure showed no alterations at low retinoid concentrations (0.125 mM), whereas at high retinoid content (1 mM), an increase of α-helix from 55% (free HSA) to 60% and a decrease of β-sheet from 22% (free HSA) to 18% occurred in the retinoid–HSA complexes. The results point to a partial stabilization of protein secondary structure at high retinoid content.

Copper(ii) complexes of terminally protected pentapeptides containing three histidyl residues in alternating positions, Ac-His-Xaa-His-Yaa-His-NH2

Copper(II) complexes of the pentapeptides Ac-HisAlaHisValHis-NH2, Ac-HisValHisAlaHis-NH2, Ac-HisProHisAlaHis-NH2, Ac-HisAlaHisProHis-NH2, Ac-HisGlyHisValHis-NH2 and Ac-HisValHisGlyHis-NH2 have been studied by potentiometric, UV-Vis, CD and EPR spectroscopic methods. It has been found that the pentapeptides are efficient ligands for the complexation with copper(II) and exhibit an outstanding versatility in the co-ordination geometry of complexes. The presence of three histidyl residues provides a high possibility for the formation of macrochelates via the exclusive binding of imidazole-N donor atoms. The macrochelation suppresses, but cannot preclude the deprotonation and metal ion co-ordination of amide functions and the species [CuH(-2)L] and [Cu2H(-4)L] predominate at physiological pH in equimolar solutions and in the presence of excess metal ions, respectively. It is also clear from the data that both C-terminal and internal histidyl residues can work as the anchoring sites for metal binding and subsequent amide deprotonation resulting in the formation of co-ordination isomers and dinuclear species in equimolar solutions and in the presence of excess metal ions, respectively. In more alkaline solutions (pH approximately 10) a third amide function can be deprotonated and co-ordinated in the species [CuH(-3)L]- with (N-,N-,N-,N(im)) co-ordination. The dinuclear species [Cu2H(-5)L]- and [Cu2H(-6)L](2-) containing hydroxide ions and/or imidazolato bridges are formed at high pH in the presence of excess of metal ions. The insertion of one proline into the sequence preceding histidyl residues hinders the deprotonation of amide functions at that site and the formation of only mononuclear complexes was observed with these peptides.

Copper(II) Interaction with Unstructured Prion Domain Outside the Octarepeat Region: Speciation, Stability, and Binding Details of Copper(II) Complexes with PrP106−126 Peptides

Copper(II) complexes of the neurotoxic peptide fragments of human and chicken prion proteins were studied by potentiometric, UV-vis, CD, and EPR spectroscopic and ESI-MS methods. The peptides included the terminally blocked native and scrambled sequences of HuPrP106-126 (HuPrPAc106-126NH2 and ScrHuPrPAc106-126NH2) and also the nona- and tetrapeptide fragments of both the human and chicken prion proteins (HuPrPAc106-114NH2, ChPrPAc119-127NH2, HuPrPAc109-112NH2, and ChPrPAc122-125NH2). The histidyl imidazole-N donor atoms were found to be the major copper(II) binding sites of all peptides; 3N and 4N complexes containing additional 2 and 3 deprotonated amide-N donors, respectively, are the major species in the physiological pH range. The complex formation processes for nona- and tetrapeptides are very similar, supporting the fact that successive deprotonation and metal ion coordination of amide functions go toward the N-termini in the form of joined six- and five-membered chelates. As a consequence, the peptide sequences investigated here, related to the neurotoxic region of the human PrP106-126 sequence, show a higher metal-binding affinity than the octarepeat fragments. In the case of the HuPrP peptide sequences, a weak pH-dependent binding of the Met109 residue was also detected in the 3N-coordinated complexes.

The effects of poly(ethylene glycol) on the solution structure of human serum albumin

Protein physical and chemical properties can be altered by polymer interaction. The presence of several high affinity binding sites on human serum albumin (HSA) makes it a possible target for many organic and polymer molecules. This study was designed to examine the interaction of HSA with poly(ethylene glycol) (PEG) in aqueous solution at physiological conditions. Fourier transform infrared, ultraviolet-visible, and CD spectroscopic methods were used to determine the polymer binding mode, the binding constant, and the effects of polymer complexation on protein secondary structure. The spectroscopic results showed that PEG is located along the polypeptide chains through H-bonding interactions with an overall affinity constant of K = 4.12 x 10(5) M(-1). The protein secondary structure showed no alterations at low PEG concentration (0.1 mM), whereas at high polymer content (1 mM), a reduction of alpha-helix from 59 (free HSA) to 53% and an increase of beta-turn from 11 (free HSA) to 22% occurred in the PEG-HSA complexes (infrared data). The CDSSTR program (CD data) also showed no major alterations of the protein secondary structure at low PEG concentrations (0.1 and 0.5 mM), while at high polymer content (1 mM), a major reduction of alpha-helix from 69 (free HSA) to 58% and an increase of beta-turn from 7 (free HSA) to 18% was observed.

Fluorinated Olefinic Peptide Nucleic Acid: Synthesis and Pairing Properties with Complementary DNA

The fluorinated olefinic peptide nucleic acid (F-OPA) system was designed as a peptide nucleic acid (PNA) analogue in which the base carrying amide moiety was replaced by an isostructural and isoelectrostatic fluorinated C-C double bond, locking the nucleobases in one of the two possible rotameric forms. By comparison of the base-pairing properties of this analogue with its nonfluorinated analogue OPA and PNA, we aimed at a closer understanding of the role of this amide function in complementary DNA recognition. Here we present the synthesis of the F-OPA monomer building blocks containing the nucleobases A, T, and G according to the MMTr/Acyl protecting group scheme. Key steps are a selective desymmetrization of the double bond in the monomer precursor via lactonization as well as a highly regioselective Mitsunobu reaction for the introduction of the bases. PNA decamers containing single F-OPA mutations and fully modified F-OPA decamers and pentadecamers containing the bases A and T were synthesized by solid-phase peptide chemistry, and their hybridization properties with complementary parallel and antiparallel DNA were assessed by UV melting curves and CD spectroscopic methods. The stability of the duplexes formed by the decamers containing single (Z)-F-OPA modifications with parallel and antiparallel DNA was found to be strongly dependent on their position in the sequence with T(m) values ranging from +2.4 to -8.1 degrees C/modification as compared to PNA. Fully modified F-OPA decamers and pentadecamers were found to form parallel duplexes with complementary DNA with reduced stability compared to PNA or OPA. An asymmetric F-OPA pentadecamer was found to form a stable self-complex (T(m) approximately 65 degrees C) of unknown structure. The generally reduced affinity to DNA may therefore be due to an increased propensity for self-aggregation.

Human serum albumin complexes with chlorophyll and chlorophyllin

Porphyrins and their metal derivatives are strong protein binders. Some of these compounds have been used for radiation sensitization therapy of cancer and are targeted to interact with cellular DNA and protein. The presence of several high-affinity binding sites on human serum albumin (HSA) makes it possible target for many organic and inorganic molecules. Chlorophyll a and chlorophyllin (a food-grade derivative of chlorophyll), the ubiquitous green plant pigment widely consumed by humans, are potent inhibitors of experimental carcinogenesis and interact with protein and DNA in many ways. This study was designed to examine the interaction of HSA with chlorophyll (Chl) and chlorophyllin (Chln) in aqueous solution at physiological conditions. Fourier transform infrared, UV-visible, and CD spectroscopic methods were used to determine the pigment binding mode, the binding constant, and the effects of porphyrin complexation on protein secondary structure. Spectroscopic results showed that chlorophyll and chlorophyllin are located along the polypeptide chains with no specific interaction. Stronger protein association was observed for Chl than for Chln, with overall binding constants of K(Chl) = 2.9 x 10(4)M(-1) and K(Chln) = 7.0 x 10(3)M(-1). The protein conformation was altered (infrared data) with reduction of alpha-helix from 55% (free HSA) to 41-40% and increase of beta-structure from 22% (free HSA) to 29-35% in the pigment-protein complexes. Using the CDSSTR program (CD data) also showed major reduction of alpha-helix from 66% (free HSA) to 58 and 55% upon complexation with Chl and Chln, respectively.

Aqueous and Micelle-bound Structural Characterization of the Epidermal Growth Factor Receptor Juxtamembrane Domain Containing Basolateral Sorting Motifs

The EGF receptor is the prototype for four highly related receptors constituting the ErbB family. The EGF receptor is normally targeted to the basolateral membrane in polarized epithelial cells, where it relays information from underlying tissues. Two basolateral sorting signals have been mapped to the cytoplasmic juxtamembrane region of the receptor, a dominant signal comprised of a polyproline core (667-PXXP) and a preceding basic residue (Arg662), and a consensus leucine-based signal (658-LL) responsible for residual sorting when the 667-PXXP signal is absent or defective. The goal of this study was to define the structure of these signals, and gain some insights into how these structures might be regulated by cellular microenvironment. Structural information was acquired for two peptides corresponding to EGF receptor residues Arg645 and Ala674 in aqueous solution or in the presence of membrane-mimicking dodecylphosphocholine micelles, using a variety of NMR and CD spectroscopic methods. Chemical shift data indicate that the 667-PXXP signal does not bind to the micelles and is in random coil state in both aqueous solution and a micellar environment, raising the possibility that 667-PXXP switches to an ordered structure during interaction with the basolateral sorting machinery. In contrast, the adjacent region including 658-LL does bind to micelles mediated by a highly positively charged region located between Arg645 and Arg656. The micelle-bound region also includes Thr654, a known substrate for PKC. This suggests a distinct mode of regulation for this signal involving membrane association and/or phosphorylation.

Synthesis of cyclopentane amide DNA (cpa-DNA) and its pairing properties.

We recently reported on the synthesis and pairing properties of the DNA analogue bicyclo[3.2.1]amide DNA (bca-DNA). In this analogue the nucleobases are attached via a linear, 4-bond amide-linker to a structurally preorganized sugar-phosphate backbone unit. To define the importance of the degree of structural rigidity of the bca-backbone unit on the pairing properties, we designed the structurally simpler cyclopentane amide DNA (cpa-DNA), in which the bicyclo[3.2.1]-scaffold was reduced to a cyclopentane unit while the base-linker was left unchanged. Here we present a synthetic route to the enantiomerically pure cpa-DNA monomers and the corresponding phosphoramidites containing the bases A and T, starting from a known, achiral precursor in 9 and 12 steps, respectively. Fully modified oligodeoxynucleotides were synthesized by standard solid-phase oligonucleotide chemistry, and their base-pairing properties with complementary oligonucleotides of the DNA-, RNA-, bca-DNA-, and cpa-DNA-backbones were assessed by UV melting curves and CD-spectroscopic methods. We found that cpa-oligoadenylates form duplexes with complementary DNA that are less stable by -2.7 degrees C/mod. compared to DNA. The corresponding cpa-oligothymidylates do not participate in complementary base-pairing with any of the investigated backbone systems except with its own (homo-duplex). As its congener bca-DNA, cpa-DNA seems to prefer left-handed helical duplex structures with DNA or with itself as indicated by the CD spectra.

Difference between Enzymatic and Chemical N-methylations of Protoberberine-Type Alkaloid, Dependent on the Stereoisomer of (−)-N-methyl-7,8,13,13a-tetrahydroberberinium Salt

Abstract A possible relation between the stereostructure of (−)-(13aS)-tetrahydroberberine (1) and its enzymatic/chemical N-methylation, an important biosynthetic reaction to isoquinoline alkaloids in plants, was examined by CD spectroscopic, X-ray crystallographic, and energy calculation methods. The CD measurements indicated that 1 has two conformers (cis and trans) concerning the ring junction of the quinolizidine skeleton, and exist with a cis/trans ratio of about 1/4 in a diethyl ether : 2-methylbutane : ethanol (5 : 5 : 2) mixture. The dimensional/conformational difference between these cis and trans conformers was clarified by the X-ray crystal-structure analyses of two stereoisomers of N-methylated 1 (3 and 4). By using these structural parameters, the progress of N-methylation was simulated by energy profile calculations, suggesting that the cis and trans conformers are the major substrate for the enzymatic and chemical N-methylation reactions, respectively. Taking these results and the simulation of N-methylation of 1 by S-adenosyl-l-methionine at the binding pocket of N-methyltransferase into consideration, different pathways for chemical and enzymatic N-methylations of 1 have been proposed.

Interaction of AZT with Human Serum Albumin Studied by Capillary Electrophoresis, FTIR and CD Spectroscopic Methods

The thymidine analoge 3′-azido-3′-deoxythymidine (AZT) is still one of the effective drugs against human immunodeficiency (HIV) infection. AZT has been used as inhibitor of HIV-1 reverse transcriptase, the virus encoded enzyme which catalyzes transcription of viral RNA to DNA. The drug interaction with protein has been included in its mechanism of action. Human serum albumin (HSA) is a carrier of many drugs in vivo and thus AZT-HSA complexation can serve as a model for drug-protein interaction. This study was designed to examine the interaction of AZT with human serum albumin at physiological conditions using constant protein concentration (0.2% or 2%) and different drug contents (5 to 1000 μM). Capillary electrophoresis, FTIR and CD spectroscopic methods were used to determine the drug binding mode, the drug binding constant and the effects of drug-HSA complexation on the protein and AZT conformations in aqueous solution. Capillary electrophoresis and spectroscopic results showed two major bindings for the AZT-HSA complexes with K1=1.9 x 106 M−1 and K2= 2.1 × 104 M−1. Minor alterations of the protein secondary structure from that of the a-helix to β-sheet were observed upon drug complexation, whereas the drug sugar pucker remained in the C2′-endo/anti conformation upon protein interaction.

Rhodium(iii) complexes with thiolate and thioether ligands derived from fac(S)-[Rh(aet)3] (aet = 2-aminoethanethiolate): selective formation, characterization and properties

Alkylation of fac(S)-[Rh(aet)3] (aet = NH2CH2CH2S−) with use of 1,2-dibromoethane in N,N-dimethylformamide produces fac(S)-[Rh(aet)(baete)]2+ ([1]2+, baete = (NH2CH2CH2SCH2)2), in which two of the three thiolato S atoms in fac(S)-[Rh(aet)3] are linked by an ethylene group. When methyl iodide is used as an alkylating reagent, two of the three thiolato S atoms are methylated to give fac(S)-[Rh(aet)(mtea)2]2+ ([2]2+, mtea = NH2CH2CH2SCH3). Complexes [1]2+ and [2]2+ were optically resolved into the two enantiomers by SP-Sephadex C-25 column chromatography. The synthesis of a trimethylated complex, fac(S)-[Rh(mtea)3]3+ ([3]3+), has been achieved by treatment of an aqueous solution of [2]2+ with dimethyl sulfate. Reactions of [1]2+ or [2]2+ with Ag+ in a 2 ∶ 1 molar ratio in water produce S-bridged RhIIIAgIRhIII trinuclear complexes, [Ag{Rh(aet)(baete)}2]5+ ([4]5+) and [Ag{Rh(aet)(mtea)2}2]5+ ([5]5+), indicating that [1]2+ and [2]2+ act as an S-donating monodentate complex-ligand. These complexes have been characterized by UV-VIS absorption, CD and NMR spectroscopic methods, together with single-crystal X-ray analyses for [1]2+ and [3]3+.

Synthesis and characterization of chiral N-O turns induced by alpha-aminoxy acids.

Chiral alpha-aminoxy acids of various side chains were synthesized with high optical purity starting from chiral alpha-amino acids. The conformations of diamides 13a-e, 15, and 16 were probed by using NMR, FT-IR, and CD spectroscopic methods as well as X-ray crystallography. The right-handed turns with eight-membered-ring intramolecular hydrogen bonds between adjacent residues (called the N-O turns) were found to be preferred for D-aminoxy acid residues, and they were independent of the side chains. The rigid chiral N-O turns should have great potential in molecular design.

Oxovanadium(IV) complexes of N-D-gluconylamino acids

The complex formation between five N-D-gluconylamino acids (the derivatives of glycine, α-L-alanine, β-alanine, L-serine and L-methionine) and VIVO ion was studied in aqueous media by means of combined pH-metric, CD, UV-Vis and EPR spectroscopic methods. The equilibrium study (25 °C, I = 0.2 mol dm−3 (KCl)) revealed the formation of various mono- and di-nuclear complexes, deprotonated to extents depending on the pH. The EPR spectra confirmed the formation of EPR-inactive complexes involving strong antiferromagnetic coupling between the metal centres in the pH interval 5–10. A dinuclear species with the composition [(VO)2L2H−4]2− predominates at pH ≈ 5 in each system; the changes in shape of the CD spectra strongly suggested the deprotonation and hence coordination of the amide nitrogen in this species. The CD results provided evidence of the metal ion-promoted deprotonation and coordination of the C(2)–OH group too under these conditions. On increase of the pH further alcoholic OH groups are deprotonated, but the amide group remains in the first coordination sphere both in the dinuclear species [(VO)2L2H−5]3− and [(VO)2L2H−6]4− and in the monomeric complex [(VO)LH−4]3−. No mononuclear bis complexes were observed, even at a high excess of ligand.

A Membrane Setting for the Sorting Motifs Present in the Adenovirus E3-13.7 Protein Which Down-regulates the Epidermal Growth Factor Receptor

The adenovirus E3-13.7 protein interferes with endosomal protein sorting to down-regulate the epidermal growth factor receptor and related tyrosine kinase receptors. The cytoplasmic C terminus of this protein contains three protein sorting motifs which are related to the function of E3-13.7. In this study, the structure of a 23-residue polypeptide corresponding to this domain was examined using solution NMR and CD spectroscopic methods. The peptide was observed to exist in a mostly random structural state in aqueous solution but underwent high affinity association with dodecylphosphocholine micelles, where it adopted an ordered structure. The affinity of this peptide for the micellar surface and the structure of the bound peptide were independent of pH variation, surface charge, or attachment of a myristoyl anchor to the N-terminal. Studies with phospholipid vesicles suggested that the micellar structural results can be extrapolated to a true lipid bilayer. On the micellar surface all three sorting motifs are closely associated with the water/apolar interface: 72-YLRH and 87-LL lie within interfacial amphipathic helices, while 76-HPQY is non-helical and dimples just above the surface. These results contribute to the development of an understanding of the basis for specificity in recognition of sorting motifs by components of the cellular protein trafficking machinery.

The first asymmetric synthesis of the naturally occurring (+)-Kotanin and the assignment of its absolute configuration

The first asymmetric synthesis of the naturally occurring (+)-Kotanin is described. The key steps involve the intramolecular oxidative coupling of the cyanocuprate intermediate and the Fries rearrangement. The absolute configuration of (+)-Kotanin was assigned as a S by CD spectroscopic method.