Synthesis of pentafluorophenyl, 2,4,5-trichlorophenyl and pentachlorophenyl esters of Fmoc-amino acids using Fmoc-amino acid chlorides as intermediates

Summary The synthesis of pentafluorophenyl, 2,4,5-trichlorophenyl and pentachlorophenyl esters of Fmoc-amino acids has been accomplished via Fmoc-amino acid chlorides as intermediates. A two phase system with a mild in-organic base (3% NaHCO₃) in the aqueous layer was used. The esterification reaction was clean and complete in about 2–3 hr. All the esters prepared have been obtained in good yield and are fully characterised.     

Solid-phase synthesis of bombesin by continuous flow procedure using Fmoc-amino acids

Bombesin has been synthesized by the continuous flow solid-phase procedure on the derivatized Kieselguhr-supported polydimethylacrylamide resin. Preformed Fmoc-amino acid symmetrical anhydrides (Met, Leu, and Arg) and Fmoc-amino acid active esters were used for amine acylation. The Mtr and the Pmc groups have been alternatively used for masking the side chain function of Arg-3. The progress of the synthesis was monitored by different analytical methods including quantitative solid-phase Edman degradation. Cleavage from the resin and simultaneous formation of the C-terminal amide function were achieved with a methanolic ammonia solution yielding indistinguishable crude peptides which have been purified by HPLC and fully characterized. Preliminary pharmacological experiments indicated that the activity of the synthetic peptides is similar to that previously measured for other synthetic bombesins. For comparison bombesin has also been prepared by solid-phase synthesis on 4-methyl benhydrylamine resin using the Boc chemistry. The results of the two strategies are discussed and compared.     

Homologation of alpha-amino acids to beta-amino acids using Fmoc-amino acid pentafluorophenyl esters.

The homologation of alpha-amino acids to beta-amino acids by the two-step Arndt-Eister method is achieved by using Fmoc-alpha-amino acid pentafluorophenyl esters for the acylation of diazomethane, synthesizing the key intermediates Fmoc-aminoacyldiazomethanes as crystalline solids in good yields and purity.     

Straight phase separation of prostaglandin methyl esters on lipophilic gels

A series of straight phase gel chromatography systems have been developed for the separation of prostaglandin methyl esters. Using the methyl esters of prostaglandins B₂, E₂, F₂α and F₂β, the basic relationships between elution volume and the polarities of the gel, the solvent system (heptane-chloroform mixtures), and the prostaglandin have been determined. The separation of prostaglandin methyl esters with slight differences in structure has been demonstrated. Examples include oxo and hydroxy prostaglandins, hydroxy epimers, double bond isomers, prostaglandins of varying α- and ω-chain length, and 1- and 2- (5,6 cis double bond) series prostaglandins. In view of the general advantages of liquid-gel chromatography, it is suggested that these systems may be useful for isolation and purification in a number of areas in the prostaglandin field.     

Biological activity of some synthetic gibberellin glucosyl esters

Four gibberellin (GA₁, GA₃, GA₄ and GA₃₇) glucosyl esters were synthesized and found to be as active as their respective free acids in the rice seedling bioassay. The rapid hydrolysis of the glucosyl esters in rice seedlings was demonstrated by feeding experiments with glucosyl esters of [³H]GA₁ and [³H]GA₄.     

Purification and Characterization of an Esterase from Micrococcus sp. YGJ1 Hydrolyzing Phthalate Esters

An esterase hydrolyzing phthalate esters has been purified from Micrococcus sp. YGJ1. The enzyme, a monomeric protein (M_r=56 kDa) with a pI of 4.0, hydrolyzes various aliphatic and aromatic carboxylesters. The medium chain (C₃-C₄) esters are the most preferred substrates. The enzyme is inhibited by HgCl₂ and p-chloromercuribenzoate but not by phenylmethyl-sulfonyl fluoride.     

Synthesis of 2-methyl-5-amino-4-oxo-3-sulfonyl esters as precursors of pseudodipeptides

Summary The synthesis of 2-methyl-5-amino-4-oxo-3-sulfonyl esters, potential precursors of XaaΨ[COCH₂]Ala, XaaΨ[E-CH=CH]Ala and XaaΨ[CH₂CH₂]Ala pseudodipeptides, has been investigated by alkylation of aminoacid-derived β-ketosulfones with ethyl 2-bromo- or 2-triflyloxypropionate in different basic conditions. Yields in 2-methyl-5-amino-4-oxo-3-sulfonyl esters are low but starting β-ketosulfones are recovered in good yield.     

Neutral lipids of leaves and stems of Trifolium repens

The neutral lipids of white clover leaves and stems have been separated into wax esters, free fatty acids, free fatty alcohols, free sterols, triglycerides and hydrocarbons. The wax esters were mainly of C₁₈ di- and tri-unsaturated fatty acids and C₃₀ fatty alcohol. Linolenic acid was the predominant free fatty acid and triacontanol was the principal free fatty alcohol. Of the hydrocarbons, C₂₉ and C₃₁ were present in the largest amounts.     

Incorporation of P32 in phosphate esters of the sugar cane plant and the effect of Si and Al on the distribution of these esters

Summary Good separation of phosphate esters labeled with P³² was obtained on paper-chromatography using the ascending technique in two dimensions at right angles.The pattern of phosphate esters in chromatographic resolution was similar for both the roots and leaves of sugar cane but there were differences in the relative proportions of the individual esters. Significant amounts of some esters, of which G-6-P constituted the main bulk, were labeled and identified after short incubation periods of excised roots in the radioactive phosphate solution.Although Al pre-treatment at the level of 0.5 mM Al₂(SO₄)₃ stimulated labeled phosphate uptake, there was no effect on the extent of phosphorylation. With Si pre-treatment, however, a significant increase in the degree of phosphorylation was noted although no effect was obtained on labeled phosphate uptake     

An efficient synthesis of mixed acid phospholipids using 1-palmitoyl-sn-glycerol-3-phosphoric acid bromoalkyl esters

The preparation of mixed-acid phospholipids is possible in high yields from 1.2-dipalmitoyl-sn-glycerol-3-phosphoric acid bromoalkyl esters. The fatty acid in the 2-position of these general intermediates for phospholipid synthesis was completely removed by hyrolysis with phospholipase A₂. The resulting 1-palmitoyl-sn-glycerol-3-phosphoric acid bromoalkyl esters were reacylated in high yields with fatty acid anhydrides in the presence of perchloric acid. Transformation of the mixed-acid phosphatidic acid bromoalkyl esters to the respective phosphatidyl cholines or -ethanolamines was possible by direct amination.     

Effect of esters based on terpenoids and GABA on fluidity of phospholipid membranes

Abstract

The influence of esters based on gamma-aminobutyric acid (GABA) and mono-/bicyclic terpenoids on membrane structure was investigated. The mechanism of action for terpenoid esters on phospholipids of artificial membranes and lipids isolated from the rat stratum corneum was studied by fluorescence and FT-IR spectroscopy. We report here, that inclusion of monocyclic terpenoid esters in phospholipid liposomes leads to growth of excimer to monomer ratio (I_E/I_M) indicating a decrease of membrane microviscosity. Another mechanism of influence on biomembranes was proposed for ester of bicyclic borneol - in this case a high ratio of vibronic peak intensities (I₁/I₃) was revealed. The addition of terpenoid esters appears in the FT-IR spectra as intensity reduction of absorption bands associated with C?=?O, P?=?O and P–O–С groups of lecithin phospholipids. Similar results were obtained after esters addition to lipids isolated from stratum corneum indicating a decrease of hydrogen bonds number between polar groups of lipids. Thus, the influence of terpenoid esters on molecular organization of the lipid matrix substantiates the feasibility of their use after transdermal delivery in vivo.     

Identification of the endogenous apolar ecdysteroid conjugates present in newly-laid eggs of the house cricket (Acheta domesticus) as 22-long-chain fatty acyl esters of ecdysone

Newly-laid eggs of the house cricket Acheta domesticus contain significant amounts of apolar ecdysteroid conjugates, which can be hydrolysed by prolonged incubation with a mixture of Helix pomatia gut hydrolases. The ecdysteroid released on hydrolysis of the apolar conjugates has been purified and identified as ecdysone by co-chromatography on normal-phase and reversed-phase HPLC and by fast-atom bombardment mass spectrometry.Starting with only 22 g newly-laid eggs (containing 16 μg conjugated ecdysone), the ecdysone conjugates have been purified by open column chromatography and four successive HPLC purification steps to give essentially pure apolar conjugates with a yield of 57%. The conjugates are shown to be a mixture of ecdysone 22-fatty acyl esters by co-chromatography with authentic reference compounds and by fast-atom bombardment mass spectrometry. The fatty acyl composition of the conjugates is very similar to that produced by the ovaries of A. domesticus from [³H]ecdysone in vitro (Whiting and Dinan, Biochem. J.252, 95–103, 1988). The major fatty acyl esters are the 22-palmitate (C_16:0), 22-oleate (C_18:1) and 22-linoleate (C_18:2), with smaller amounts of the myristate (C_14:0), stearate (C_18:0) and arachidate (C_20:0) esters.This report constitutes the first identification from an insect source of endogenous ecdysteroid 22-fatty acyl esters, which have previously been identified in ticks and as metabolites of exogenous [³H]ecdysone in several arthropod species.     

Papain-catalysed hydrolysis of some hippuric esters. A new mechanism for papain-catalysed hydrolyses

1. The Michaelis–Menten parameters for the papain-catalysed hydrolysis of a number of alkyl, aryl and alkyl-thiol esters of hippuric acid have been determined. 2. For all the aryl esters and most of the alkyl esters studied, the catalytic constant, k₀, is 2–3sec.⁻¹ and most probably represents deacylation of the common intermediate, hippuryl-papain. 3. Two alkyl esters and hippurylamide, however, have catalytic rate constants, k₀, less than 2–3sec.⁻¹. It is possible to interpret all the available kinetic data in terms of a three-step mechanism in which an enzyme–substrate complex is first formed, followed by acylation of the enzyme through an essential thiol group, followed by deacylation of the acyl-enzyme. 4. The logarithm of the ratio of the Michaelis–Menten parameters, which reflect the acylation rate constant, for four aryl esters of hippuric acid studied give a linear Hammett plot against the substituent constant, σ. Arguments are presented that indicate acid as well as nucleophilic catalysis in the acylation process and that the most likely proton donor is an imidazolium ion. 5. It is suggested that this imidazolium ion is part of the same histidine residue that has been tentatively implicated in the deacylation process (Lowe & Williams, 1965b). 6. A new mechanism is proposed for the papain-catalysed hydrolysis of N-acyl-α-amino acid derivatives.     

Cloning,Heterologous Expression,and Enzymatic Characterization of Cathepsin L from Starfish (Asterina pectinifera)

Methyl esters of 3-epi-GA₃ and 3-epi-GA₁ were efficiently prepared from methyl esters of GA₃ and GA₁ respectively, by highly selective epimerization of the 3-hydroxyl function with a base in a low-polar aprotic medium.     

Fatty acids. part 42 The preparation and properties of methyl monomercaptostearates. some related thiols, and some methyl epithiostearates

Some saturated and unsaturated mercapto C₁₈ esters have been obtained for the first time. Such compounds are prepared from hydroxy esters via their mesyloxy derivatives by reaction with sodium hydrogen sulphide or with potassium thioacetate (followed by deacetylation) or from alkene esters by radical addition of thioacetic acid. The mercapto esters are readily identified by infrared, nuclear magnetic resonance, and mass spectroscopic procedures, preferably after acetylation or trifluoroacetylation.γ-Mesyloxy alkenes furnish tetrahydrothiophen rather than mercapto alkenes and methyl 9,12-epithiostearate was synthesised by an independent route from thiophen.     

Differentiation of human promyelocytic leukemia cells is accompanied by an increase in insulin receptors

Changes in insulin receptors accompanying cell differentiation in human promyelocytic leukemia cells (HL-60) were studied. Cell differentiation was induced by 1α,25-dihydroxyvitamin D₃, vitamin A, dimethyl sulfoxide, or phorbol esters. 1α,25-dihydroxy-vitamin D₃ increased the ability of HL-60 cells to bind insulin in a dose-dependent manner. The increase in insulin binding was due to an increase in the number of insulin receptors. Vitamin A, dimethyl sulfoxide and phorbol esters were also effective in increaseing insulin receptors. Thus, the differentiation of HL-60 cells was accompanied by an increase in insulin receptors.     

Lipids of four species of freshwater dinoflagellates

The steroidal derivatives, fatty acid alkyl esters and triacylglycerols have been identified in two cultured dinoflagellates, Woloszynskia coronata and Ceratium furcoides, and natural populations of two species, Peridinium lomnickii and P. cinctum. Within each species, the same sterol moieties occurred in free and esterified forms, but the species differed in the proportion of 4α-methyl and desmethyl sterols. Both groups occurred in the two Peridinium species, whereas W. coronata contained only 4α-methylsterols and C. furcoides, uniquely among dinoflagellates analysed to date, contained only desmethylsterols, although these were analogues of 4α-methylsterols present in the other species. 4α-Methyl steroidal ketones were present in P. lomnickii and W. coronata; cholest-4-en-3-one and 5α-cholestan-3-one were detected in C. furcoides, but no steroidal ketones were detected in P. cinctum. Methyl and ethyl esters of fatty acids (C₁₂C₁₈) were detected in three species, in P. cinctum the ethyl esters were dominant, while phytyl esters occurred only in the Peridinium spp. The molecular composition of triacylglycerols containing only saturated and monoenoic acyl groups was determined by GC-MS. Lower carbon number constituents from W. coronata contained a C₄ acyl group, previously found only in animal milk fats.     

Phorbol esters inhibit alpha1 adrenergic stimulation of glycogenolysis in isolated rat hepatocytes

Tumor promoting phorbol esters can stimulate Ca⁺⁺-phospholipid-dependent protein kinase. It has been suggested that this enzyme may mediate the effects of calcium-dependent hormones. In this paper the effects of phorbol 12-myristate 13-acetate (TPA) on isolated rat hepatocyte metabolism were studied. Phorbol esters completely blocked alpha₁-adrenergic stimulation of glycogenolysis. This effect is quite specific for alpha₁-adrenergic actions, as the stimulations of glycogenolysis by vasopressin, angiotensin II, ionophore A-23187 and glucagon were unaffected by TPA. The potencies of the different phorbol esters used in this study suggests that the inhibitory effects of these agents may be due to activation of protein kinase C. The effect of phorbol esters on alpha₁-adrenergic actions seems to occur at an early step of the alpha₁-adrenergic action. TPA (10^?11–10^?6M) was unable to stimulate glycogenolysis. Urea synthesis, which is stimulated by vasopressin and alpha₁-adrenergic agents, was not stimulated by phorbol ester, neither alone nor in combination with the Ca⁺⁺ ionophore A-23187.     

Enhancement of fruity aroma production of Pseudomonas fragi grown on skim milk,whey and whey permeate supplemented with C3-C7 fatty acids

Summary Pseudomonas fragi strain CRDA 037 produced a fruity aroma when grown in skim milk-, whey-and whey permeate-based culture media. The production of the odour-active metabolites was related to the lipid content of these media but was not influenced by the pH of the cultures. Analysis of the fruity aroma revealed that esters of fatty acids were some of the odouractive metabolites. Addition of C₃-C₇ fatty acids to the culture at 0 h stimulated the production of the corresponding fatty acid esters from 12 to 1570 times compared to unsupplemented media. Supplementation of the culture media with the C₃-C₇ fatty acids at 48 h, resulted in a 1.4- to 932-fold increase in the ethyl ester concentration.