Application of fluorescamine XII. Chiroptical properties of fluorescamine condensation compounds with some less common α-amino acids

Fluorescamine (FLURAM^®) reacts efficiently with less common chiral α-amino acids to form pyrrolinone-type chromophores. The characteristic Cotton effects at 324-300 and at 290-263 nm can be related to the absolute configuration of the parent α-amino acid without isolation of the products. These CD bands are negative and positive, respectively, for the derivatives of the L-α-amino acids.     

An Efficient Synthesis Of Acyclic N7- and N9-Adenine Nucleosides Via Alkylation With Secondary Carbon Electrophiles to Introduce Versatile Functional Groups At the C-1 Position of Acyclic Moiety

The introduction of versatile functional groups, allyl and ester, at the C-1 position of the acyclic chain in acyclic adenine nucleosides was achieved for the first time directly by alkylation of adenine and N⁶-protected adenine. Thus, the C-1′-substituted N⁹-adenine acyclic nucleoside, adenine-9-yl-pent-4-enoic acid ethyl ester (11), was prepared by direct alkylation of adenine with 2-bromopent-4-enoic acid ethyl ester (6), while the corresponding N⁷-regioisomer, 2-[6, (dimethylaminomethyleneamino)-purin-7-yl]-pent-4-enoic acid ethyl ester (10), was obtained in one step by the coupling of N,N-dimethyl-N′- (9H-purin-6-yl)-formamidine (9) with 2-bromopent-4-enoic acid ethyl ester (6). The functional groups, ester and allyl, were converted to the desired hydroxymethyl and hydroxyethyl groups, and subsequently to phosphonomethyl derivatives and corresponding pyrophosphorylphosphonates.     

Whole‐cell biotransformation of oleanolic acid by free and immobilized cells of Nocardia iowensis: Characterization of new metabolites

In this study, Nocardia iowensis was used to transform oleanolic acid (OA) into oleanane derivatives. The first derivative, which was found after 24 h of cultivation, was the known and already described OA methyl ester. After 1 week, two other derivatives (oleanonic acid methyl ester and an unknown metabolite) were identified as new products of a biotransformation by N. iowensis. These oleanane metabolites were characterized by HPLC, HPLC‐ESI‐MS, and HPLC‐¹H NMR spectroscopy. The biotransformation was performed by suspended and immobilized cells (ICs) of N. iowensis. Cells immobilized in alginate beads were used in order to prepare a continuous process. The substrate uptake of free and ICs was similar, whereas the peak area of OA methyl ester of the ICs was only about 10% of the native cells. However, the final product (oleanonic acid methyl ester) concentrations were similar in both approaches, whereas the unknown metabolite 3 was only detected transiently in the medium of ICs. Based on these results, a new biosynthetic pathway for the biotechnological production of oleanonic acid methyl ester is proposed.     

Circular dichroism studies on alpha- and beta-ketosides of 5-acetamido-3,5-dideoxy-D-glycero-D-galacto- nonulopyranosonic acid (N-acetylneuraminic acid) and of some of its derivatives.

The circular dichroism spectra of a number of N-acetylneuraminic acid derivatives in aqueous solution were studied. For all compounds, the Cotton effects were found to be in the spectral range of the acetamido and carboxyl chromophores. The c.d. curves of the methy, ethyl, and allyl alpha-D-ketosides are characterized by a broad, positive band centered at lambda similar to 195 nm with a slight skew towards the higher wavelengths and weak bands between lambda 225 and 255 nm, whereas the methyl beta-D-ketoside and the corresponding methyl ester show only an intense positive band with a broad shoulder in the same spectral range. 5-Acetamido-3,5-dideoxy-D-glycero-beta-D-galacto-nonulopyranose, its methyl beta-D-ketoside, and 5-acetamido-3,5-dideoxy-D-glycero-D-galacto-nonulopyranosonamide containing only the acetamido chromophore showed one single positive Cotton effect centered at lambda similar to 192 nm. The c.d. spectrum of 5-acetamido-3,5-dideoxy-D-glycero-D-galacto-nonulopyranosonic acid confirms the beta-D configuration of the free acid in aqueous solution, whereas the shape of the c.d. curve of O-(N-acetyl-alpha-D-neuraminopyranosyl)-(2yields3)-O-beta-D-galactopyranosyl-(1 yields 4)-D-glucopyranose resembles that of the methyl, ethyl, and allyl alpha-D-ketosides 2-4.     

Biosynthesis of ursolic acid derivatives by microbial metabolism of ursolic acid with Nocardia sp. strains—Proposal of new biosynthetic pathways

Our studies of the microbial-metabolism of triterpenoid ursolic acid by various Nocardia sp. strains, have led to the proposal of two novel pathways to produce triterpenoid derivatives. Nocardia sp. NRRL 5646, Nocardia sp. 44822 and Nocardia sp. 44000 generated the following ursolic acid derivatives: ursolic acid methyl ester, ursonic acid, ursonic acid methyl ester, 3-oxoursa-1,12-dien-28-oic acid and 3-oxoursa-1,12-dien-28-oic acid methyl ester. Nocardia sp. 45077 synthesized ursonic acid and 3-oxoursa-1,12-dien-28-oic acid while Nocardia sp. 46002 produced only ursonic acid and Nocardia sp. 43069 showed no metabolism at all. The conversion of ursolic acid by Nocardia sp. NRRL 5646 was independent of the medium used for the fermentation. An increase in temperature from 28 °C to 36 °C doubled the reaction rate of the biotransformation. The analysis of ursane metabolites was done by HPLC, while their structures were established using HPLC–APCI_pos-MS/MS and HPLC–NMR spectroscopy. The pseudo molecular ion peaks were determined by HPLC–APCI_pos-MS and used to measure their molecular weight. The product ion spectra of the metabolites showed the characteristic fragments of Δ¹²-oleanes and Δ¹²-ursanes indicating that a substitution in ring A or B was responsible for the decrease in molecular weight.Based on these results, two new biosynthetic pathways are proposed. These new pathways can presumably be used as strategic routes for the biotechnological production of triterpenoid derivatives. It is assumed that a 3β-hydroxysteroid dehydrogenase and a 3-ketosteroid-Δ¹-dehydrogenase are involved in the transformation of the steroid.     

Studies on 2-aziridinecarboxylic acid peptides: Their reaction and uses

The reaction of 2-aziridinecarboxylic acid derivatives with several protic reagents was used to synthesize depsipeptides, dehydroamino acid derivatives, diaminopropionic acid derivatives, and phospho peptide derivatives. The reaction of N-aminoacyl-2-aziridinecarboxylic acid benzyl ester with amino acid ester induced stereoselective transacylation.     

Circular dichroism spectroscopy of 2-aminotetralins

The circular dichroism (CD) spectra of a series of oxygenated 2-(dipropylamino)tetralin derivatives are reported. On the basis of known absolute configurations and conformational preferences of the compounds, the validity of published correlations between the sign of the ¹L_b Cotton effect and the three-dimensional structure was examined. Contrary to predictions, substitution in position 6 or 7 of the tetralin moiety did not change the sign of the ¹L_b Cotton effect. An unexpected sign inversion was, however, observed in some of the compounds containing methyl substituents in the nonaromatic ring. The occurrence of this inversion was not correlated with a change in conformational behaviour and varied depending on the position and nature of the aromatic substituent. No correlations were obvious between the sign of the ¹L_b Cotton effect and the absolute configuration and conformational preferences of the compounds. Therefore, at present, CD spectroscopy does not appear to be useful in assignments of the absolute configurations of 2-(dipropylamino)tetralin derivatives. © 1995 Wiley-Liss, Inc.     

Electronic Trap States in Methanofullerenes

The trap states in three fullerene derivatives, namely PC₆₁BM ([6,6]‐phenyl C₆₁ butyric acid methyl ester), bisPC₆₁BM (bis[6,6]‐phenyl C₆₁ butyric acid methyl ester) and PC₇₁BM ([6,6]‐phenyl C₇₁ butyric acid methyl ester), are investigated by means of thermally stimulated current measurements (TSC). Thereby, the lower limit of the trap densities for all studied methanofullerenes is on the order of 10²² m^?3, with the highest trap density in bisPC₆₁BM and the lowest in PC₆₁BM. Fractional TSC measurements on PC₆₁BM reveal a broad trap distribution instead of discrete trap levels, with activation energies ranging from 15 meV to 270 meV and the maximum at about 75 meV. The activation energies of the most prominent traps in the other two fullerene derivatives are significantly higher, at 96 meV and 223 meV for PC₇₁BM and 184 meV for bisPC₆₁BM, respectively. The influence of these findings on the performance of organic solar cells is discussed.     

Sterically hindered disulfide bridges in cystine diketopiperazine, cysteinyl-cysteine disulfide and derivatives.

L-Cystine diketopiperazine (1), L-cysteinyl-cysteine disulfide -HCl (2), L-cysteinyl-cysteine disulfide methyl ester -HCl (3), and t-butyloxycarbonyl-L-cysteinyl-cysteine disulfide methyl ester (4) are investigated by CD, ultraviolet, 13C NMR, infrared and laser Raman spectroscopy. The temperature dependence of the 13C NMR signals of 1 reveals an exceptionally high energy barrier of deltaGNo. = 15.8 +/- 0.2 kcal/mol for the reversible change in helicity of the inherently dissymmetric disulfide bridge of 1. The P-helical diastereomer predominates in dimethyl-sulfoxide at 25 degrees C, with 80-85% of the molecules having this configuration. The Cotton effects of 1 are larger and show smaller temperature coefficients than the conformationally more mobile cystine compounds 2 and 3. After dissolving crystals of 1 in 95% ethanol there is a time-dependent decrease of the ellipticity of the negative Cotton effect at 225 nm, indicating a conformational change in going from crystal to solution. Besides 1, 2 and 3 are at present the only known examples of cystine derivatives with C-S-S-C torsional angles around 90 degrees, which do not exhibit optical activity in the long wavelength disulfide absorption, as is predicted for 1 from the Linderberg-Michl model. At 305 nm a new weak Cotton effect was discovered for 1. The solvent dependence of the CD spectra is discussed and the infrared and Raman spectra are assigned.     

Chemical modification of ribonucleosides with N-acetyl-3,5-di[125I]iodotyrosyl hydrazide

Several 3,5-diiodotryrosyl derivatives have been synthesized by both sodium iodideiodine and the sodium iodide-iodic acid methods. Conditions optimizing yield and purity of the product have been established for the latter reaction. Under those conditions, treatment of N-acetyl-tyrosyl ethyl ester with sodium [¹²⁵I]iodide and iodic acid gave N-acetyl-3,5-di[¹²⁵I]iodotyrosyl ethyl ester (ADITEE) with high specific activity. Hydrazination of [¹²⁵I]ADITEE produces N-acetyl-3,5-di[¹²⁵I]iodotyrosyl hydrazide. This hydrazide has been successfully used to modify four different ribonucleoside dialdehydes.     

A circular dichroism study of modified nucleosides

The conformation of 5-methoxycarbonylmethyluridine and 5-methoxycarbonylmethyl-2-thiouridine was studied by means of circular dichroism in various solvents. In order to calculate the accurate spectral parameters of the Cotton effects, the circular dichroism spectra were resolved into component Gaussian functions which simultaneously fit the adsorption spectra. On the basis of circular dichroism and proton magnetic resonance spectra, these nucleosides were found to occur in the β-configuration with the ³E-gg-anti conformation preferred. Due to the fact that the long-wavelength Cotton effect of mcm⁵s²U is not masked by the Cotton effects of the other nucleic acid monomers, the molecular parameters of this band may be useful for the conformational analysis of tRNA segments.     

Synthesis and Immunostimulating Activity of Cysteine-Containing Derivatives of Glycyrrhizic Acid

New cysteine-containing derivatives of glycyrrhizic acid were synthesized by its coupling with Cys(Bzl) esters or the Cys(Bzl)-Val-OBu ^t dipeptide by the active ester method (DCC/HOSu) or by Woodward's reagent K. The derivatives with Cys(Bzl) and Cys(Bzl)-Val residues attached to the carbohydrate part of the molecule stimulated the primary immune response and the reaction of delayed-Type hypersensitivity in mice at a dose of 2 mg/kg.     

Analysis of warfarin enantiomers: Chromatographic separation of six stereoisomeric esters prepared from (−)-(1S,2R,4R)-endo-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hept-5-ene-2- carboxylic acid

Reaction of rac-warfarin, (?)-(1S,2R,4R)-endo-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hept-5-ene-2- carboxylic acid [(?)-HCA] and carbodiimide reagents gave two noncyclic ketonic diastereoisomeric derivatives whereas rac-warfarin and (?)-HCA acid chloride with 4-(dimethylamino)pyridine gave four cyclic hemiketal diastereoisomeric ester derivatives. The structure and stereochemistry of diastereoisomeric esters prepared from warfarin and p-chlorowarfarin were determined from ¹H- and ¹³C-NMR spectra, mass spectra, and hydrolysis to warfarin and p-chlorowarfarin enantiomers. The structure and stereochemistry of one of the cyclic hemiketal diastereoisomeric derivatives of warfarin are supported by an X-ray crystallographic determination. Mechanisms for the formation of all products are proposed. © 1994 Wiley-Liss, Inc.     

Separation and detection of uv-absorbing derivatives of fecal bile acid metabolites by high-performance liquid chromatography

Major fecal bile acid metabolites related to lithocholic acid were resolved by high-performance liquid chromatography (hplc). The uv-absorbing p-nitrobenzyl ester derivatives of lithocholic, isolithocholic, 3-keto-5β-cholanic, and 5β-cholanic acids were prepared using the reagent o,p-nitrobenzyl-N,N′-diisopropylisourea. Separation was achieved in less than 20 min on a microparticulate silica column using isocratic elution with 2% isopropanol in isooctane as the mobile phase. The p-chlorobenzoyl esters of methylated lithocholic and isolithocholic acids were also prepared but required purification by thin-layer chromatography before separation by hplc. These derivatives were eluted from a Porasil T column using 5% diisopropyl ether in isooctane as the mobile phase. Lithocholic and isolithocholic acids produced by microbial metabolism of [¹⁴COOH]taurolithocholic acid were separated and identified by preparing p-nitrobenzyl derivatives and monitoring the column effluent for both uv and radioactivity. This technique is a rapid and sensitive method for isolating bile acid metabolites.     

Inhibitory effect of 8-substituted adenosine derivatives on Ca++ and modulator protein-dependent phosphodiesterase activity.

8-Substituted adenosine and cyclic AMP derivatives exhibited some negative Cotton effects in circular Dichroism at B_2u band in pH 7.5 solution, suggesting that these derivatives take syn conformation. The adenosine derivatives, as well as cyclic AMP derivatives, competitively inhibited the cyclic AMP hydrolyzing activity in Ca⁺⁺ and modulator protein-dependent phosphodiesterase preparation from hog brain cortex. The inhibitory potential of an adenosine derivative was lower than that of the cyclic AMP derivative having the same substituent by the lack of the phosphate moiety for which affinity was 0.5 kcal / mol. These results may suggest that the cyclic AMP hydrolyzing site on the enzyme requires the syn conformation of purine riboside.     

3-([3-125I]iodo-4-hydroxyphenyl)propionyl carbohydrazide,a new radioiodination reagent for ultrasensitive detection and determination of periodate-oxidized nucleoside derivatives and other carbonyl compounds

A new radioiodination reagent for the identification and quantitation of periodate-oxidized ribonucleosides was developed. The reagent, 3-([3-¹²⁵I]iodo-4-hydroxyphenyl)propionyl carbohydrazide, was prepared by radioiodination of 3-(4-hydroxyphenyl)propionic acid N-hydroxysuccinimide ester in the presence of chloramine T, followed by reduction of the latter with sodium arsenite and treatment of the radioiodinated ester with an excess of carbohydrazide. The reagent reacted quantitatively with periodate-oxidized nucleosides to form ¹²⁵I-labeled morpholine derivatives which were separated by thin-layer chromatography and quantitated by liquid scintillation counting. The reagent was found to react also with other carbonyl compounds and thus may find more general application in the qualitative and quantitative ultramicroanalysis of aldehydes and ketones.     

Inhibitory Effects of Caffeic Acid Phenethyl Ester Derivatives on Replication of Hepatitis C Virus

Caffeic acid phenethyl ester (CAPE) has been reported as a multifunctional compound. In this report, we tested the effect of CAPE and its derivatives on hepatitis C virus (HCV) replication in order to develop an effective anti-HCV compound. CAPE and CAPE derivatives exhibited anti-HCV activity against an HCV replicon cell line of genotype 1b with EC₅₀ values in a range from 1.0 to 109.6 µM. Analyses of chemical structure and antiviral activity suggested that the length of the n-alkyl side chain and catechol moiety are responsible for the anti-HCV activity of these compounds. Caffeic acid n-octyl ester exhibited the highest anti-HCV activity among the tested derivatives with an EC₅₀ value of 1.0 µM and an SI value of 63.1 by using the replicon cell line derived from genotype 1b strain Con1. Treatment with caffeic acid n-octyl ester inhibited HCV replication of genotype 2a at a similar level to that of genotype 1b irrespectively of interferon signaling. Caffeic acid n-octyl ester could synergistically enhance the anti-HCV activities of interferon-alpha 2b, daclatasvir, and VX-222, but neither telaprevir nor danoprevir. These results suggest that caffeic acid n-octyl ester is a potential candidate for novel anti-HCV chemotherapy drugs.     

Coupling of iminodiacetic acid with amino acid derivatives in solution and solid phase

The IR studies for the preactivation step of N-protected iminodiacetic acid with different coupling reagents (TCFH,TFFH, HATU, HBTU, HSTU) were reported here and showed theformation of an anhydride as an active intermediate in caseof TCFH and TFFH. The formation of a mixture of an anhydrideand an active ester (–OBt, –OAt or –OSu) were observed forHBTU, HATU or HSTU coupling reagent. Dependent on the couplingconditions, acylation of N-protected iminodiacetic acid with amino acid ester or amide derivatives in solution phase gavemono- or di-substituted iminodiacetic acid derivatives. Couplingof N-protected iminodiacetic acid with an amino acid or peptideattached to a solid support (PAL-PEG-PS or Wang resin) gave onlythe monosubstituted iminodiacetic acid derivatives.     

Steric analysis of glycerophospholipids by circular dichroism. Stereospecifity of phospholipase D catalyzed transesterification.

The circular dichroism spectra of natural glycerophospholipids and synthetic 1-$\text{sn}$-phosphatidic acid were recorded. 3-$\text{sn}$-phosphatidic acid derivatives were found to show a positive Cotton effect, while 1-$\text{sn}$-phosphatidic acid revealed a negative Cotton effect. The results are interpreted in terms of the carboxyl sector rule. By this method phospholipase D was shown to produce stereospecifically 3-$\text{sn}$-phosphatidyl-1-$\text{sn}$-glycerol when incubated with egg yolk lecithin and exess of glycerol.     

Catechol-based inhibitors of bacterial urease

Targeted covalent inhibitors of urease were developed on the basis of the catechol structure. Forty amide and ester derivatives of 3,4-dihydroxyphenylacetic acid, caffeic acid, ferulic acid and gallic acid were obtained and screened against Sporosarcinia pasteurii urease. The most active compound, namely propargyl ester of 3,4-dihydroxyphenylacetic acid exhibited IC₅₀?=?518?nM and$k_{\mathit{inact}}/K_i$?=?1379?M^?1?s^?1. Inhibitory activity of this compound was better and toxicity lower than those obtained for the starting compound – catechol. The molecular modelling studies revealed a mode of binding consistent with structure-activity relationships.