- Selective Decarbonylation of Fatty Acid Esters to Linear α-Olefins
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Selective decarbonylation of p-nitrophenol esters of fatty acids to the corresponding linear α-olefins (LAOs) was achieved using palladium catalysis. After extensive ligand screening, a mixed-ligand system exploiting the trans-spanning diphosphine XantPhos and an N-heterocyclic carbene (IPr) was identified as the most effective in yielding high α-selectivity and high conversions of the ester (>98% selectivity, >90% conversion using 2.5 mol % of PdCl2 and 5 mol % of the ligands, 190 °C, 2-2.5 h). On the basis of insights from modeling at the density functional level of theory, we propose that the mixed-ligand set achieves high α-selectivity by promoting olefin dissociation from the palladium center following β-hydride elimination, which is especially facilitated both by the combined steric bias of the mixed-ligand set and by the ability of the XantPhos ligand to coordinate in both mono- and bidentate fashions.
- John, Alex,Dereli, Büsra,Ortunìo, Manuel A.,Johnson, Hillis E.,Hillmyer, Marc A.,Cramer, Christopher J.,Tolman, William B.
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p. 2956 - 2964
(2017/08/21)
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- Enzyme mediated-transesterification of verbascoside and evaluation of antifungal activity of synthesised compounds
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Enzymatic acylation of verbascoside, a polyhydroxylated natural product, has been reported in this study using five different commercial lipases and taking p-nitrophenyl alkanoates as acyl donors. Out of these enzymes, the immobilised Candida antarctica lipase B was found as the enzyme of choice. Mono-and di-acylated products were formed, with mono as major product indicating high regioselective nature of such transformations. A series of acyl esters of verbascoside have been synthesised by this enzymatic transesterification methodology. The lipophilicity of the synthesised analogues was also checked. The analogues were further subjected to synergistic antifungal activity with amphotericin B (AmB) against Candida albicans. Fourfold reduction in minimum inhibitory concentration of AmB was observed with few synthesised analogues such as verbascoside 4″-octanoate (3b), verbascoside 4″-palmitate (3d) and verbascoside 4″,4′-dipalmitate (4d) at a concentration of 0.5 g/mL.
- Khazir, Jabeena,Ali, Intizar,Khan, Inshad Ali,Sampath Kumar, Halmuthur Mahabalarao
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p. 727 - 734
(2015/09/23)
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- Fatty acid-binding site environments of serum vitamin D-binding protein and albumin are different
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Vitamin D-binding protein (DBP) and albumin (ALB) are abundant serum proteins and both possess high-affinity binding for saturated and unsaturated fatty acids. However, certain differences exist. We surmised that in cases where serum albumin level is low, DBP presumably can act as a transporter of fatty acids. To explore this possibility we synthesized several alkylating derivatives of 14C-palmitic acid to probe the fatty acid-binding pockets of DBP and ALB. We observed that N-ethyl-5-phenylisooxazolium-3′-sulfonate-ester (WRK-ester) of 14C-palmitic acid specifically labeled DBP; but p-nitrophenyl- and N-hydroxysuccinimidyl-esters failed to do so. However, p-nitrophenyl ester of 14C-palmitic acid specifically labeled bovine ALB, indicating that the micro-environment of the fatty acid-binding domains of DBP and ALB may be different; and DBP may not replace ALB as a transporter of fatty acids.
- Swamy, Narasimha,Ray, Rahul
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p. 165 - 168
(2008/09/21)
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- Synthesis of Ceramide Analogues Having the C(4)-C(5) Bond of the Long-Chain Base as Part of an Aromatic or Heteroaromatic System
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Two efficient and stereoselective methods are described for the preparation of aryl and heteroaryl ceramide analogues 2 and 3. The first route involves the addition of an aryllithium or a heteroaryllithium reagent (7a or 25a, respectively) to the L-serine-derived aldehyde 4, followed by hydrolysis of the oxazolidine, liberation of the amino group, and N-acylation. The second route, which was used to prepare arylceramide analogue 2 in eight steps and 28% overall yield starting with 3-bromobenzaldehyde, utilizes a Heck reaction to afford (E)-α,β-unsaturated ester 16, then osmium-catalyzed asymmetric dihydroxylation for the introduction of the desired chirality at C-2 and C-3. Regioselective α-azidation of α-O-nosyl-β-hydroxyester 18 with sodium azide, followed by LiAlH4 reduction of the azido and ester groups and N-acylation, complete the synthesis of arylceramide analogue 2.
- Chun, Jiong,He, Linli,Byun, Hoe-Sup,Bittman, Robert
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p. 7634 - 7640
(2007/10/03)
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- HIGHER N-ACYL-L-AMINO ACID DERIVATIVES
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A preparative method is proposed for obtaining higher N-acylamino acids by reaction of free amino acids with fatty acid nitrophenyl esters.It was shown that these acids can transport positive ions through a liquid lipophilic medium.A direct method is proposed for obtaining fatty acid 4-nitrophenyl esters by boiling 4-nitrophenol and the fatty acid in xylene in a Soxhlet apparatus in the presence of an acid catalyst.
- Kochetkov, K. A.,Urmambetova, Zh. S.,Belikov, V. M.,Bakasova, Z. B.
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p. 2311 - 2316
(2007/10/02)
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- SYNTHESES OF D-ERYTHRO-1-DEOXYDIHYDROCERAMIDE-1-SULFONIC ACID AND PHOSPHONOSPHINGOGLYCOLIPID FOUND IN MARINE ORGANISM VIA A COMMON PRECURSOR
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D-Erythro-1-deoxydihydroceramide-1-sulfonic acid, isolated from alkali-stable hydrogenated lipids in a non-photosynthetic marine diatom, Nitzschia alba, and (2S,3R)-N-palmitoyl-1-O--β-D-galactopyranosyl>-D-sphingosine, found in marine snail Turbo cornutus were synthesized via a common precursor (10) starting from galactose.
- Ohashi, Kinji,Kosai, Shunji,Arizuka, Mitsuo,Watanabe, Takashi,Yamagiwa, Yoshiro,et al.
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p. 2557 - 2570
(2007/10/02)
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- Synthesis and Biological Activity of the Isomers and Analogs of (4E,8E,2S,3R,2'R)-N-2'-Hydroxyhexadecanoyl-9-methyl-4,8-sphingadienine, the Ceramide Portion of the Fruiting-inducing Cerebroside in a Basidiomycete Schizophyllum commune
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The title compounds were synthesized by employing 2-aminohexadecanoic acid and serine as the chiral sources, and served for an assay of fruiting-inducing activity on Schizophyllum commune.The structure-bioactivity relationship among closely related synthetic ceramides is discussed.
- Funaki, Yuji,Kawai, Genshiro,Mori, Kenji
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p. 615 - 624
(2007/10/02)
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- CHIMIE DES SUCRES SANS GROUPEMENTS PROTECTEURS-I-ESTERIFICATION REGIOSELECTIVE DE L'HYDROXYLE ANOMERE DU LACTOSE, DU MALTOSE ET DU GLUCOSE
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Treatment of acyl chlorides 4 with mercaptothiazoline, mercaptobenzothiazole, p-nitrophenol and 8-hydroxyquinoline in the presence of Et3N, afforded high yields of the corresponding reactive amides 5a-h,S-thioesters 6e-h and aryl esters 7e-h and 8a-h, respectively.The esters 6e-h, 7e-h and 8e-h reacted with excess β-lactose in pyridine, to give the corresponding β-esters 9e-h resulting from esterification of the anomeric hydroxyl of the sugar.The amides 5c, f-h gave the α-lactosyl esters 9c, f-h.The amide 5e and the esters 8b, c, e reacted with β-maltose, thus affording the corresponding β-maltosyl esters 10b, c, e, whereas the compounds 8a-e reacted with β-glucose, yielding the corresponding β-glucosyl esters 11a-e.This appears to be one of the very few selective chemical modifications of sugars known, which do not involve the toilsome protection-deprotection methology.The now commercially available maltosyl and glucosyl esters 10e and 11d-e are new non-ionic, and water soluble detergents which could be used for studies of cell membrane proteins.
- Plusquellec, Daniel,Roulleau, Fabienne,Bertho, Francoise,Lefeuvre, Martine,Brown, Eric
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p. 2457 - 2468
(2007/10/02)
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- the Effect of Hydrophobic-Lipophilic Interactions on Chemical Reactivity. 1. New Evidence for Intermolecular Aggregation and Self-Coiling
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The hydrolytic behavior of 21 para-substituted phenyl esters of n-alkanoic acids (n-X) with various chain lengths in 60:40 (Φ=0.60), 50:50 (Φ=0.50), and 40:60 v/v (Φ=0.40) Me2SO-H2O mixtures was studied.Four new sets of experimental results which include departure from Hammett correlation for N-hexadecanoates (16-X), substantial differences in activation parameters, and effects of amylose on the kinetic parameters and on the activation parameters are presented along lines of reasoning mentioned by previous authors.These data establish that the aggregation and self-coiling of the n-alkanoate chain actually exist under experimental conditions.
- Jiang, Xi-Kui,Hui, Yong-Zheng,Fan, Wei-Qiang
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p. 3839 - 3843
(2007/10/02)
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- CHIMIE DES SUCRES SANS GROUPEMENTS PROTECTEURS: ESTERIFICATION REGIOSELECTIVE DE L'HYDROXYLE ANOMERE DU LACTOSE LIBRE
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Treatment of α-lactose with acyl chlorides failed to give any pure products.However, the anomeric hydroxyl of lactose was esterified selectively and in high yields, by treating the free sugar with reactive acylating agents such as N-acyl thiazolidine-thiones or esters of p-nitrophenol, mercapto-benzothiazole and 8-hydroxy quinoline, making thus unnecessary the preliminary protection of the other hydroxyls of the lactose molecule.This appears to be one of the very few selective modifications of sugars known, which do not involve the classical protection-deprotection methodology.
- Roulleau, Fabienne,Plusquellec, Daniel,Brown, Eric
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p. 719 - 722
(2007/10/02)
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- CATALYTIC EFFICIENCY OF SYNTHETIC MICELLAR CATALYSTS BEARING A MERCAPTO GROUP AS THE REACTION CENTER.
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In order to obtain a clue to understanding the micro-environmental effect on the reactivity of a mercapto group placed in a reaction center of enzymes, micellar surfactants bearing a mercapto group were synthesized and their catalytic activity in the degradation of p-nitrophenyl carboxylates was studied. N-Hexadecyl-N** alpha -glutaryl-L-cysteinamide (AM multiplied by (times) Cys-1) has an ability to form anionic micelles in aqueous media. The catalytic activity of AM multiplied by (times) Cys-1 was compared with that of another synthetic surfactant, N-hexadecanoyl-L-cysteine (AM multiplied by (times) Cys-2). These surfactants below their critical micelle concentations markedly accelerated the degradation of several p-nitrophenyl carboxylates. On the contrary, the concentration-rate profiles for the degradation of p-nitrophenyl dodecanoate (PNPL) as catalyzed by the surfactants indicate that the reactivity of the mercapto group is reduced upon formation of the anionic micelles.
- Murakami,Nakano,Matsumoto
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p. 2996 - 3004
(2007/10/05)
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- N-acyl and desamino human calcitonin and analogs thereof
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The new hypocalcaemically active peptides of formula I and corresponding compounds in which one or more of the asparagine and glutamic acid radicals are replaced by the aspartic acid or glutamic acid radical and/or the aspartic acid radical is replaced by the asparagine radical, their dimers, especially those in which 2 identical peptide sequences (1-32 and 1'-32') are joined in an anti-parallel arrangement via the cysteine radicals 1,7' and 7,1' by means of a disulfide bond, and derivatives are useful as hypocalcaemic agents and are prepared by splitting off groups protecting at least one amino or one carboxyl group or oxidizing the corresponding sulfides to the disulfides or condensing together adequate peptides.
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