Alkyl-linked diglycerides inhibit protein kinase C activation by diacylglycerols

Alkylacylglycerols are synthesized when choline-phospholipids are degraded by a phospholipase C. This class of compounds has been shown to have biological activities; however, the mechanism of action is unknown. A series of alkyl-linked diglycerides were synthesized and tested for activity in an in vitro assay for protein kinase C. When protein kinase C activity was stimulated with the synthetic diacylglyceride analog 1-oleoyl-2-acetyl-sn-glycerol, the addition of alkyl glycerides caused a concentration-dependent inhibition of protein kinase C activity. Comparison of the protein kinase C inhibition by this series of 1-O-alkyl-2-acyl analogs revealed that both saturated and unsaturated long-chain groups in position 1 were effective and that dietherglycerols with short-chain moieties in position 2 were also effective. It is concluded from these studies that the biological activity of alkyl-linked glycerides may be expressed through protein kinase C inhibition.

Molecular species composition of the major phospholipids in brain and retina from rainbow trout (Salmo gairdneri). Occurrence of high levels of di-(n-3)polyunsaturated fatty acid species

The molecular-species compositions of the diacyl classes of the major phospholipids from the brain and retina of rainbow trout (Salmo gairdneri) were determined. A total of 46 possible species was identified. Didocosahexaenoyl species were major components of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS) from retina, comprising 14.1, 41.3 and 28.3% of the respective totals. This species was also abundant in PE and PS from brain, accounting for 14.9 and 19.9% of the totals respectively. Small amounts of di-polyunsaturated fatty acid species [C22:6(n-3) with C20:5(n-3), and C22:6(n-3) with C22:5(n-3)] were also found in these phospholipids. Phosphatidylinositol (PI) from both tissues contained no di-polyunsaturated fatty acid species. Retinal PI contained 40.1% C18:0-C20:4(n-6) with 14.9% of C18:0-C20:5(n-3); brain PI contained 42.3% of C18:0-C20:5 and 10.4% of C18:0-C20:4 species. Brain PC contained a substantial amount of nervonic acid-containing species with the pair C18:1-C24:1/C24:1-C18:1 comprising 8.9% of the total.

The synthesis of chiral glycerides starting from D- and L-serine

A method for synthesizing chiral glycerides starting from L- or D-serine is described. Optically-active serine (both enantiomers are commerically available) was transformed into glyceric acid by stereospecific diazotization. The configuration at carbon atom 2 was maintained during the reaction. The glyceric acid was then converted into optically pure isopropylideneglycerol - which is an important intermediate in the synthesis of mono-, di- and triglyderides - by esterification followed by acetalization with acetone and reduction with lithium aluminium hydride. Reaction of this intermediate with triphenylphosphine in tetrachloromethane followed by acid-catalysed hydrolysis and dehydrohalogenation provided optically-active glycidol (2,3-epoxy-1-propanol). The epoxy ring of an ester of glycidol and a fatty acid was then opened stereospecifically with retention of configuration by heating the glycidol ester in the presence of a second fatty acid and a catalyst. This yielded a chiral 1,3-diglyceride which could be converted into a chiral triglyceride.

Transmembrane movement of phosphatidylglycerol and diacylglycerol sulfhydryl analogues

Transmembrane movement of phospholipids is a fundamental step in the process of biological membrane assembly and intracellular lipid sorting. To facilitate study of transmembrane movement, we have synthesized analogues of phosphatidylglycerol and diacylglycerol in which a sulfhydryl group replaces a hydroxyl group in the polar head group. A rapid, continuous assay for the movement of phospholipids across single-walled lipid vesicles was developed that exploits the reactivity of these analogues toward 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), a nonpenetrating, colorimetric, sulfhydryl reagent. In the reaction of DTNB with vesicles containing phosphatidylthioglycerol, a phosphatidylglycerol analogue, two kinetic phases were seen, which represent the reaction of DTNB with phosphatidylthioglycerol in the outer and inner leaflets of the bilayer. Analysis of the slow second phase indicated that the half-time for phosphatidylthioglycerol transbilayer movement was in excess of 8 days. In a similar experiment using dioleoylthioglycerol, a diacylglycerol analogue, the reaction was complete within 15 s. The large difference in translocation rates between these two lipids indicates that the primary barrier to transmembrane movement is the polar head group and implies that phospholipid translocation events in biological membranes may not be unlike those for molecules similar to the polar head groups alone.

Synthetic diacylglycerols (DAG) and DAG-lactones as activators of protein kinase C (PK-C)

The central role of protein kinase C (PK-C) in cellular signal transduction has established it as an important therapeutic target for cancer and other diseases. We have developed a series of 4,4-disubstituted-gamma-butyrolactones, which contain a constrained glycerol backbone (DAG-lactones) and behave as potent and selective activating ligands of PK-C with affinities that approach those of the structurally complex natural product agonists, such as the phorbol esters. This Account traces the design and construction of these molecules. Initially, we examined the consequences of reducing the entropic penalty associated with the transformation of a DAG into a DAG-lactone. Then, using molecular modeling to extend insights arising from the newly solved crystal structure of a C1 domain complexed with phorbol ester, we incorporated amino acid-specific branched hydrophobic chains to provide a new generation of DAG-lactones that have the capacity to bind to PK-C with low nanomolar affinity. Depending on the specific pattern of hydrophobic substitution, some DAG-lactones are able to induce selective translocation of individual PK-C isozymes to different cellular compartments, and since the specific nature of these hydrophobic interactions influences biological outcome, some of these compounds exhibit cell-specific antitumor activity. The ability to direct specific PK-C isozyme translocation with sets of structurally simple, yet highly potent molecules provides a powerful tool for engineering a plethora of molecules with novel biological functions.

Pyridinium Cationic Lipids in Gene Delivery: A Structure−Activity Correlation Study

Three series of pyridinium cationic lipids useful as nonviral gene delivery agents were prepared by reaction of pyrylium salts with aminodiols, followed by acylation with fatty acyl chlorides. On the basis of this set of compounds, we undertook a comprehensive structure-activity relationship study at the level of the linker, hydrophobic anchor, and counterion in order to identify the structural elements that generate the highest transfection efficiency for this new type of cationic lipid. The results revealed that when formulated with cholesterol at a 1:1 molar ratio, the 1-(1,3-dimyristoyloxyprop-2-yl)-2,4,6-trimethylpyridinium, under the form of hexafluorophosphate (5AMyr) or chloride (5DMyr), was able to transfect NCI-H23 lung carcinoma with efficiencies surpassing classic DOTAP-based formulations and with lower cytotoxicity. Subsequent tests on other malignancies yielded similarly promising results.

Production of bioadditives from glycerol esterification over zirconia supported heteropolyacids

The synthesis of bioadditives for biofuels from glycerol esterification with acetic acid was performed over zirconia supported heteropolyacids catalysts using H(4)SiW(12)O(40) (HSiW), H(3)PW(12)O(40) (HPW) and H(3)PMo(12)O(40) (HPMo) as active compounds. The as-prepared catalysts were characterized by N(2)-physisorption, XRD, Raman spectroscopy, NH(3)-TPD, FTIR of pyridine adsorption and H(2)O-TPD. Among the catalysts tested, HSiW/ZrO(2) achieved the best catalytic performance owing to the better combination of surface Brønsted acid sites and hydrothermal stability. A 93.6% combined selectivity of glyceryl diacetate and glyceryl triacetate with complete glycerol conversion was obtained at 120°C and 4h of reaction time in the presence of HSiW/ZrO(2). This catalyst also presented consistent activity for four consecutive reaction cycles, while HPW/ZrO(2) and HPMo/ZrO(2) exhibited distinct deactivation after reusability tests. In addition, HSiW/ZrO(2) can be resistant to the impurities present in bulk glycerol.

Immunocytochemical evidence for translocation of protein kinase C in human megakaryoblastic leukemic cells: synergistic effects of Ca2+ and activators of protein kinase C on the plasma membrane association

Immunological analysis using monoclonal antibodies against subspecies of protein kinase C revealed the predominant expression of the isozyme, type II, in human megakaryoblastic leukemic cells. We investigated the effects of phorbol diester 12-O-tetradecanoyl phorbol-13-acetate (TPA), the Ca2+ ionophore ionomycin and synthetic diacylglycerol 1-oleoyl-2-acetylglycerol (OAG) on the immunocytochemical localization of protein kinase C in these cells. Indirect immunofluorescence techniques revealed the enzyme to be located in a diffuse cytosolic pattern, in the intact cells. When the cells were exposed to 100 nM TPA, the immunofluorescent staining was translocated from the cytoplasm to the plasma membrane. The translocation was protracted and staining on the membrane decreased in parallel with the Ca2+, phospholipid-dependent protein kinase activity. Treatment of the cells with 500 nM ionomycin caused an apparent translocation comparable with that seen with TPA, however, this translocation was transient and most of the cytosolic staining was within 60 min. We also found that 30 micrograms/ml OAG did not have significant effects on distribution of the staining, but rather acted synergistically on the translocation with the suboptimal concentration of 100 nM ionomycin. A similar synergism was also observed with 10 nM TPA and 100 nM ionomycin. These results obtained in situ provide evidence that intracellular Ca2+ and diacylglycerol regulate membrane binding of the enzyme in vivo.

Phospholipid-nucleoside conjugates. 3. Syntheses and preliminary biological evaluation of 1-beta-D-arabinofuranosylcytosine 5'-monophosphate-L-1,2-dipalmitin and selected 1-beta-D-arabinofuranosylcytosine 5-diphosphate-L-1,2-diacylglycerols

Several new phospholipid-ara-C conjugates have been prepared and tested as prodrugs of the parent ara-C. The new derivative include ara-CMP-L-dipalmitin, ara-CDP-L-distearin, ara-CDP-L dimyristin, ara-CDP-L-diolein, and the radioactively labeled derivative ara-CDP-L-di[1-14C]palmitin. In addition, the unusually stable ara-CMP-L-dipalmitin-N-phosphoryldicyclohexylurea adduct was isolated as a crystalline solid (two diastereomers) in the reaction sequence to prepare ara-CMP-L-dipalmitin. The new prodrugs were solubilized by sonication methods and tested for their antiproliferative activity in vitro against mouse myeloma MPC-11 cells and against L1210 lymphoid leukemia. Such studies demonstrated that the antiproliferative activities of the prodrugs (as determined by ED50) were less that ara-C on a molar basis. In the mouse myeloma cell line some evidence was obtained that the antiproliferative activity was related to the chain length of the fatty acid side chains in the prodrugs. In in vivo studies against L1210 lymphoid leukemia in mice, the prodrugs were shown to be much more effective than ara-C, with the overall efficacy apparently being independent of the length of the fatty acid side chain. Some evidence was obtained in the vivo studies that the ara-CDP-L-dimyristin, which bears the shortest fatty acid side chain, was more toxic at the higher dosages than the longer chain length derivatives.

Synthesis and anti-herpes simplex viral activity of monoglycosyl diglycerides

Based on the discovery of antiviral beta-galactosyl diglycerides from Clinacanthus nutans leaves, 19 monoglycosyl diglycerides were synthesized and examined for inhibitory effect on herpes simplex virus types 1 and 2 (HSV-1, HSV-2). A study of the structure-activity relationships of the synthetic monoglycosyl diglycerides indicated that the fatty acyl moieties were critical for inhibitory action with higher activity displayed as the acyl groups became more olefinic in character. The sugar moiety was also important for anti-HSV action; however, the type of sugar (glucose or galactose) did not affect activity. The stereochemistry at C-2 of the glycerol backbone displayed no significant effect on anti-HSV activity. Among the compounds synthesized, 1,2-O-dilinolenoyl-3-O-beta-D-glucopyranosyl-sn-glycerol showed the highest inhibitory activity against HSV-1 and HSV-2 with IC50 values of 12.5+/-0.5 and 18.5+/-1.5 microg/ml, respectively.

The physical properties of glycosyl diacylglycerols. Calorimetric, X-ray diffraction and Fourier transform spectroscopic studies of a homologous series of 1,2-di-O-acyl-3-O-(beta-D-galactopyranosyl)-sn-glycerols

We have synthesized a homologous series of saturated 1,2-di-O-n-acyl-3-O-(beta-D-galactopyranosyl)-sn-glycerols with odd- and even-numbered hydrocarbon chains ranging in length from 10 to 20 carbon atoms, and have investigated their physical properties using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The DSC results show a complex pattern of phase behaviour, which in a typical preheated sample consists of a lower temperature, moderately energetic lamellar gel/lamellar liquid-crystalline (L(beta)/L(alpha)) phase transition and a higher temperature, weakly energetic lamellar/nonlamellar phase transition. On annealing at a suitable temperature below the L(beta)/L(alpha) phase transition, the L(beta) phase converts to a lamellar crystalline (L(c1)) phase which may undergo a highly energetic L(c1)/L(alpha) or L(c1)/inverted hexagonal (H(II)) phase transition at very high temperatures on subsequent heating or convert to a second L(c2) phase in certain long chain compounds on storage at or below 4 degrees C. The transition temperatures and phase assignments for these galactolipids are supported by our XRD and FTIR spectroscopic measurements. The phase transition temperatures of all of these events are higher than those of the comparable phase transitions exhibited by the corresponding diacyl alpha- and beta-D-glucosyl glycerols. In contrast, the L(beta)/L(alpha) and lamellar/nonlamellar phase transition temperatures of the beta-D-galactosyl glycerols are lower than those of the corresponding diacyl phosphatidylethanolamines (PEs) and these glycolipids form inverted cubic phases at temperatures between the lamellar and H(II) phase regions. Our FTIR measurements indicate that in the L(beta) phase, the hydrocarbon chains form a hexagonally packed structure in which the headgroup and interfacial region are undergoing rapid motion, whereas the L(c) phase consists of a more highly ordered, hydrogen-bonded phase, in which the chains are packed in an orthorhombic subcell similar to that reported for the diacyl-beta-D-glucosyl-sn-glycerols. A comparison of the DSC data presented here with our earlier studies of other diacyl glycolipids shows that the rate of conversion from the L(beta) to the L(c) phase in the beta-D-galactosyl glycerols is slightly faster than that seen in the alpha-D-glucosyl glycerols and much faster than that seen in the corresponding beta-D-glucosyl glycerols. The similarities between the FTIR spectra and the first-order spacings for the lamellar phases in both the beta-D-glucosyl and galactosyl glycerols suggest that the headgroup orientations may be similar in both beta-anomers in all of their lamellar phases. Thus, the differences in their L(beta)/L(c) conversion kinetics and the lamellar/nonlamellar phase properties of these lipids probably arise from subtly different hydration and H-bonding interactions in the headgroup and interfacial regions of these phases. In the latter case, such differences would be expected to alter the ability of the polar headgroup to counterbalance the volume of the hydrocarbon chains. This perspective is discussed in the context of the mechanism for the L(alpha)/H(II) phase transition which we recently proposed, based on our X-ray diffraction measurements of a series of PEs.

Structure and polymorphism of saturated monoacid 1,2-diacyl-sn-glycerols

The 1,2-diacyl-sn-glycerols (1,2-DGs) are the predominant naturally occurring isomer found in cell membranes, lipid droplets, and lipoproteins. They are involved in the metabolism of monoacylglycerols, triacylglycerols, and phospholipids. The 1,2-DGs participate in the activation of protein kinase C, in phosphorylation of target proteins, and in transduction of extracellular signals into the cell. We have undertaken a study of the physical properties of a homologous series of synthetic optically active diacylglycerols. Stereospecific 1,2-diacyl-sn-glycerols were synthesized with saturated fatty acyl chains of 12, 16, 18, 22, and 24 carbons in length. Their polymorphic behavior was examined by differential scanning calorimetry and X-ray powder diffraction. The solvent-crystallized form for all the 1,2-DGs packs in the orthorhombic perpendicular subcell (beta') and melts with a single sharp endotherm to an isotropic liquid. On quenching, the C12, C16 and C18 compounds pack in a hexagonal subcell (alpha), whereas the C22 and C24 pack in a pseudohexagonal subcell (sub-alpha). The sub-alpha phase reversibly converts to the alpha phase. The long spacings of these compounds in both the alpha and beta' phases increase with chain length. In the alpha and beta' phases, the acyl chain tilts were found to be 90 degrees and 62 degrees from the basal methyl plane. The polymorphic behavior of 1,2-diacyl-sn-glycerol is quite different from that of the corresponding monoacid saturated 1,3-diacylglycerols which form two beta phases with triclinic parallel subcells.

Activation of TRPC6 calcium channels by diacylglycerol (DAG)-containing arachidonic acid: A comparative study with DAG-containing docosahexaenoic acid

We synthesized a diacylglycerol (DAG)-containing arachidonic acid, i.e., 1-stearoyl-2-arachidonyl-sn-glycerol (SAG), and studied its implication in the modulation of canonical transient receptor potential sub-type 6 (TRPC6) channels in stably-transfected HEK-293 cells. SAG induced the influx of Ca(2+), and also of other bivalent cations like Ba(2+) and Sr(2+), in these cells. SAG-evoked Ca(2+) influx was not due to its metabolites as inhibitors of DAG-lipase (RHC80267) and DAG-kinase (R50922) failed to inhibit the response of the same. To emphasise that SAG exerts its action via its DAG configuration, but not due to the presence of stearic acid at sn-1 position, we synthesized 1-palmitoyl-2-arachidonyl-sn-glycerol (PAG). PAG-induced increases in [Ca(2+)](i) were not significantly different from those induced by SAG. For the comparative studies, we also synthesized the DAG-containing docosahexaenoic acid, i.e., 1-stearoyl-2-docosahexaenoyl-sn-glycerol (SDG). We observed that SDG and 1,2-dioctanoyl-sn-glycerol (DOG), a DAG analogue, also evoked increases in [Ca(2+)](i), which were lesser than those evoked by SAG. However, activation of TRPC6 channels by all the DAG molecular species (SAG, DOG and SDG) required Src kinases as the tyrosine kinase inhibitors, PP2 and SU6656, significantly attenuated the increases in [Ca(2+)](i) evoked by these agents. Moreover, disruption of lipid rafts with methyl-beta-cyclodextrin completely abolished SAG-, DOG- and SDG-induced increases in [Ca(2+)](i). The present study shows that SAG as well as SDG and DOG stimulate Ca(2+) influx through the activation of TRPC6 calcium channels which are regulated by Src kinases and intact lipid raft domains.

Ultrasound irradiation promoted efficient solvent-free lipase-catalyzed production of mono- and diacylglycerols from olive oil

This work reports the enzymatic production of mono- and diacylglycerols under the influence of ultrasound irradiation, in a solvent-free system, with and without the presence of surfactants at a constant temperature of 65°C, glycerol to oil molar ratio of 2:1 and a commercial immobilized lipase (Novozym 435) as catalyst. For this purpose, two operation modes were adopted: the use of a sonotrode (ultrasonic probe), without agitation, varying reaction time, irradiation amplitude (25-45% of the total power) and type of surfactant, and a mechanically stirred reactor (600 rpm) under ultrasound irradiation in a water bath, testing different surfactants. Results show that very satisfactory MAG and DAG yields, above 50 wt.%, can be obtained without the use of surfactant, at mild irradiation power supply (∼130 W), with no important enzyme activity losses verified, in a relatively short reaction time (2h), and low enzyme content (7.5 wt.%). Also, reaction kinetic results show that contents of MAG+DAG as high as ∼65 wt.% can be achieved at longer times (6h), indicating a promising route for producing MAG and DAG using ultrasound irradiation.

A versatile, flexible synthesis of 1,3-diglycerides and tryglycerides

A flexible method for synthesising 1,30diflycerides and triglycerides is described. Glycidol esters, prepared by a known route from epichlorohydrin and the sodium salt of a fatty acid, were heated with another or with the same fatty acid and a quaternary ammonium salt. This resulted in a fast, mild reaction and higher yields and greater purity of the diglycerides than hitherto obtained in this synthesis. The mixture of 1,3- and 1,2-diglycerides obtained was isomerised by heating while still in the solid phase to 1,3-diglycerides. Triglycerides were prepared from the diglycerides by acylation using a fatty acid chloride and pyridine in hexane.

Response of cardiac myocytes to a ramp increase of diacylglycerol generated by photolysis of a novel caged diacylglycerol

To test the responsiveness of living cells to the intracellular messenger diacylglycerol, we developed a prototype caged diacylglycerol compound, 3-O-(alpha-carboxyl-2,4-dinitrobenzyl)-1 ,2-dioctanoyl-rac-glycerol (designated alpha-carboxyl caged diC(8)), that produces dioctanoylglycerol (diC(8)) on photolysis. Alpha-Carboxyl caged diC(8) is biologically inert toward diacylglycerol kinase and protein kinase C in vitro and is readily incorporated into cardiac myocyte membranes, where it has no effect before irradiation. Exposure to near-UV light releases biologically active diC8 in good yield (quantum efficiency = 0.2). Here we examine a cellular response to controlled elevation of diC8 within single cardiac myocytes. Twitch amplitude was monitored in electrically stimulated myocytes, and a ramp increase in the concentration of diC(8) was generated by continuous irradiation of cells loaded with the caged compound. The myocyte response was biphasic with a positive inotropic phase (39% increase in twitch amplitude), followed by a large negative inotropic phase (>80% decrease). The time to peak inotropy for both phases depended on the light intensity, decreasing from 376 +/- 51 S to 44 +/- 5 s (positive phase) and 422 +/- 118 S to 51 +/- 9 S (negative phase) as the light intensity was increased eightfold. Both phases were inhibited by the protein kinase C inhibitor chelethyrine chloride. An increase in extracellular K+ from 5 mM to 20 mM to partially depolarize the cell membrane eliminated the positive inotropic phase, but the negative inotropic response was largely unaltered. The results reveal new features in the response of cardiac muscle to diacylglycerol, including a positive inotropic phase and a complex responsiveness to a simple linear increase in diacylglycerol. The effects of photoreleased diC(8) were similar to the effects of opiate agonists selective for kappa receptors, consistent with a major role for diacylglycerol in these responses.

Conformationally constrained analogues of diacylglycerol. 10. Ultrapotent protein kinase C ligands based on a racemic 5-disubstituted tetrahydro-2-furanone template

5,5-Bis(hydroxymethyl)tetrahydro-2-furanone and its isomer 4,4-bis(hydroxymethyl)tetrahydro-2-furanone were investigated as possible templates for the construction of conformationally constrained analogues of the biologically important second messenger, diacylglycerol (DAG). The former lactone contains embedded within its structure an exact glycerol moiety, while in the latter the ring oxygen has been transposed to the other side of the carbonyl group. All target compounds were synthesized as racemates from 1,3-dihydroxy-2-propanone. The 5,5-bis(hydroxymethyl)tetrahydro-2-furanone proved to be the better template for the construction of DAG surrogates that were demonstrated to have high binding affinities for the biological target, protein kinase C (PK-C). The simplest target compounds derived from this template (3e and 3f) have one of the hydroxyl moieties functionalized either as a myristate or as an oleate ester. The simplest target compound (9c) derived from the ineffective 4,4-bis-(hydroxymethyl)tetrahydro-2-furanone template was investigated only with a myristoyl acyl chain. Reducing the long acyl chain to an acetyl moiety and attaching a compensating lipophilic chain to the lactone ring as an alpha-alkylidene moiety produced compounds 10e and 10f (Z-isomers) and 11e and 11f (E-isomers), which were constructed on the more effective 5,5-bis(hydroxymethyl)tetrahydro-2-furanone template. Targets 14c (Z-isomer) and 15c (E-isomer) were derived, in turn, from 4,4-bis(hydroxymethyl)tetrahydro-2-furanone. The affinities of these ligands for PK-C were assessed in terms of their ability to displace bound [3H-20]phorbol 12,13-dibutyrate (PDBU) from the single isozyme PK-C alpha. The biological data support the hypothesis that the increase in binding affinity for PK-C shown by some of these constrained DAG mimetics appears to be entropic in nature. Two of the designed ligands (10e and 10f) showed the highest affinities (34 and 24 nM, respectively) reported so far for a DAG analogue. Assuming that the interaction between these racemic compounds and PK-C is stereospecific, the potency of the active enantiomer is anticipated to double.

The solvent influence on the positional selectivity of Novozym 435 during 1,3-diolein synthesis by esterification

The influence of solvents with a wide range of log P (from -0.23 to 4.5) on the positional selectivity of the immobilized lipase Novozym 435 during the esterification of oleic acid with glycerol for 1,3-diolein preparation was investigated. Analysis was performed on the basis of a simplified kinetic model of 1,3-diolein synthesis. The results showed that the preferential selectivity of Novozym 435 to 1-position over 2-position of the glycerol molecular became weaker and weaker with the increasing log P of the solvent. But after one 1-position was acylated, the preferential selectivity to the other 1-position over 2-position would be enhanced strongly for each solvent. The study also revealed that relatively hydrophilic solvent such as t-butanol was an ideal solvent for Novozym 435 catalyzed 1,3-diolein synthesis through esterification of oleic acid with glycerol.

Inhibition of microbial lipases with stereoisomeric triradylglycerol analog phosphonates

1,2(2,3)-Diradylglycero O-(p-nitrophenyl) n-hexylphosphonates were synthesized, with the diradylglycerol moiety being di-O-octylglycerol, 1-O-hexadecyl-2-O-pyrenedecanylglycerol, or 1-O-octyl-2-oleoyl-glycerol, and tested for their ability to inactivate lipases from Chromobacterium viscosum (CVL) and Rhizopus oryzae (ROL). The experimental data indicate the formation of stable, covalent 1:1 enzyme-inhibitor adducts with the di-O-alkylglycero phosphonates. The differences in reactivity of diastereomeric phosphonates with opposite configuration at the glycerol backbone was less expressed with both enzymes tested as compared to the influence of the stereochemistry at the phosphorus. Both lipases exhibited the same preference for the chirality at the phosphorus that was independent from the absolute configuration at the glycerol backbone. However, with CVL and ROL the inhibitors with the active site serine-directed phosphonate linked at position sn-1 of the glycerol moiety reacted significantly faster than the corresponding sn-3 analogs, reflecting the sn-1 stereopreference of the enzymes towards triacylglycerol analogs with a sn-2 O-alkyl substituent. In contrast, the phosphonates based on the 1-O-octyl-2-oleoylglycerol did not significantly inactivate CVL. Unexpectedly, these substances were hydrolyzed in the presence of lipase.

An optimized protein kinase C activating diacylglycerol combining high binding affinity (Ki) with reduced lipophilicity (log P)

A small, focused combinatorial library encompassing all possible permutations of acyl branched alkyl chains-small and large, saturated and unsaturated-was generated from the active diacylglycerol enantiomer (S-DAG) to help identify the analogue with the highest binding affinity (lowest Ki) for protein kinase C (PK-C) combined with the minimum lipophilicity (log P). The selected ligand (3B) activated PK-C more effectively than sn-1,2-dioctanoylglycerol (diC8) despite being 1.4 log units more hydrophilic. Compound 3B indeed represents the most potent, hydrophilic DAG ligand to date. With the help of a green fluorescent protein (GFP)-tagged PK-Calpha, 3B was able to translocate the full length protein to the membrane with an optimal dose of 100 microM in CHO-K1 cells, while diC8 failed to achieve translocation even at doses 3-fold higher. Molecular modeling of 3B into an empty C1b domain of PK-Cdelta clearly showed the existence of a preferred binding orientation. In addition, molecular dynamic simulations suggest that binding discrimination could result from a favorable van der Waals (VDW) interaction between the large, branched sn-1 acyl group of 3B and the aromatic rings of Trp252 (PK-Cdelta) or Tyr252 (PK-Calpha). The DAG analogue of 3B in which the acyl groups are reversed (2C) showed a decrease in binding affinity reflecting the capacity of PK-C to effectively discriminate between alternative orientations of the acyl chains.

Ultrasonic pretreatment promotes diacylglycerol production from lard by lipase-catalysed glycerolysis and its physicochemical properties

The objective of this study was to evaluate the effect of ultrasonic pretreatment on diacylglycerol (DAG) synthesis by lipase-catalysed glycerolysis of lard and to analyse the physicochemical properties of lard-based DAG. The optimal ultrasonic pretreatment conditions were: Rhizomucor miehei (Lipozyme® RMIM)-to-lard ratio 4:100 (W/W), 45 °C for 5 min, and power 250 W. The lard-based DAG samples for 4 h of glycerolysis reactions with ultrasonic pretreatment (named DAG-U) and 11 h of glycerolysis reactions without ultrasonic pretreatment (named DAG-N) had similar DAG contents and were used for further analysis. The major FA compositions and iodine value of lard, DAG-U and DAG-N were similar. Fourier transform infrared spectroscopy analysis proved that enzymatic glycerolysis with and without ultrasonic pretreatment did not change the structure of the lard. Differential scanning calorimetry analysis showed that the crystallization onset of DAG-U and DAG-N shifted to higher temperatures than that of lard, which indicated that DAG oils accelerated nucleation and crystal growth. X-ray diffraction analysis revealed that both DAG-U and DAG-N contained β' crystal and a substantially lower amount of β crystal. Overall, ultrasonic pretreatment promotes diacylglycerol production from lard through lipase-catalysed glycerolysis, and DAG-U and DAG-N have similar physicochemical properties.

Syntheses of an α-d-Gal-(1→6)-β-d-Gal diglyceride, as lipase substrate

Two different routes were explored to afford 3-O-(6-O-alpha-D-galactopyranosyl-beta-D-galactopyranosyl)-1,2-di-O-dodecanoyl-sn-glycerol. In the first one, the key step was the glycosylation of the 3-O-(2,3,4-tri-O-benzyl-beta-D-galactopyranosyl)-1,2-O-isopropylidene-sn-glycerol acceptor with 2-pyridyl 2,3,4,6-tetra-O-benzyl-1-thio-beta-D-galactopyranoside as the donor. In the second one, the key step was the coupling of 2,3,4-tri-O-acetyl-6-O-(2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl)-D-galactopyranosyl trichloroacetimidate donor with 1,2-O-isopropylidene-sn-glycerol. Even though the number of steps was the same in both pathways, the first one afforded a better overall yield (12.4%) than the second one (6.5%). This eight-step synthesis allowed the preparation of the expected glycolipid, which was used as substrate for recombinant GPLRP2 galactolipase using the monomolecular film technique.

Conformationally constrained analogues of diacylglycerol (DAG). 17. Contrast between sn-1 and sn-2 DAG lactones in binding to protein kinase C

In previous work, we have obtained potent protein kinase C (PK-C) ligands with low-namomolar binding affinities by constructing diacylglycerol (DAG) mimetics in which the sn-2 carbonyl of DAG was constrained into a lactone ring. An additional structural element that helped achieve high binding affinity was the presence of branched acyl or alpha-alkylidene chains. In the present study, the effects of similarly branched chains on a different lactone system, where the lactone carbonyl is now equivalent to the sn-1 carbonyl of DAG, are investigated. In this new lactone template, the two chiral centers must have the S-configuration for enzyme recognition. As with the sn-2 DAG lactones, the branched chains were designed to optimize van der Waals contacts with a group of conserved hydrophobic amino acids located on the rim of the C1 domain of PK-C. The acyl and alpha-alkylidene chains were also designed to be lipophilically equivalent (8 carbons each). Eight new compounds (7-14) representing all possible combinations of linear and branched acyl and alpha-alkylidene were synthesized and evaluated. The sn-1 DAG lactones were less effective as PK-C ligands than the sn-2 DAG lactones despite having a similar array of linear or branched acyl and alpha-alkylidene chains

Conformationally constrained analogues of diacylglycerol. 12. Ultrapotent protein kinase C ligands based on a chiral 4,4-disubstituted heptono-1,4-lactone template

Conformationally constrained analogues of diacylglycerol (DAG) built on a 5(-)[(acyloxy)methyl]-5-(hydroxymethyl)tetrahydro-2-furanone template (1, Chart 1) were shown previously to bind tightly to protein kinase C alpha (PK-C alpha) in a stereospecific manner. These compounds, however, racemized readily through rapid acyl migration and lost biological potency. In order to circumvent this problem, the "reversed ester" analogues were designed as a new set of PK-C ligands. This reversal of the ester function produced some new DAG mimetics that are embedded in a C-4 doubly-branched heptono-1,4-lactone template. The reversed ester analogues were impervious to racemization, and their chemically distinct branches facilitated the enantiospecific syntheses of all targets. Compound 2, the simplest reversed ester analogue of 1 (Chart 1), exhibited a 3.5-fold reduction in binding affinity toward PK-C alpha which we attributed to the loss of a stabilizing gauche interaction that caused the ester branch in 2 to be more disordered than in the normal ester 1. However, conversion of the propanoyl branch of 2 into a propenoyl branch restored binding affinity (3 versus 5). As expected, the compounds bound to the enzyme with strict enantioselectivity (3 and 5 versus 4 and 6). Functionalization of the propenoyl-branched compounds as alpha-alkylidene lactones, in a manner which proved successful with the 5(-)[(acyloxy)methyl]-5-(hydroxymethyl)tetrahydro-2-furanone template (9 and 10), produced stable compounds with equivalent ultrapotent binding affinities for PK-C alpha (7 and 8). The additional incorporation of the propenoyl-branched carbonyl into a gamma-lactone ring was performed (11-14) not only to derive a possible additional entropic advantage but also to confirm the spatial disposition of this carbonyl function in the ligand-enzyme complex. Although no additional entropic advantage was derived, the high binding affinities displayed by compounds 11 and 12 helped to establish the correct orientation of the equivalent carbonyl group in PK-C-bound DAG. As expected, these DAG analogues activated PK-C alpha. The most potent agonist, compound 8, stimulated phosphorylation of the alpha-pseudosubstrate peptide, and in primary mouse keratinocytes it caused inhibition of binding of epidermal growth factor with an ED50 of approximately 1 microM. In contrast to the phorbol esters, compound 8 did not induce acute edema or hyperplasia in skin of CD-1 mice, and its pattern of downregulation with several PK-C isozymes was different from that of phorbol 12-myristate 13-acetate (PMA).

Diacylglycerol-rich domain formation in giant stearoyl-oleoyl phosphatidylcholine vesicles driven by phospholipase C activity

We have studied the effect of phospholipase C from Bacillus cereus and Clostridium perfringens (alpha-toxin) on giant stearoyl-oleoyl phosphatidylcholine (SOPC) vesicles. Enzyme activity leads to a binary mixture of SOPC and the diacylglycerol SOG, which phase separates into a SOPC-rich bilayer phase and a SOG-rich isotropic bulk-like domain embedded within the membrane, as seen directly by phase contrast microscopy. After prolonged enzymatic attack, all bilayer membranes are transformed into an isotropic pure SOG phase as characterized by fluorescence microscopy, differential scanning calorimetry, fluorescence anisotropy measurements, and small angle x-ray scattering. These domains may have biological relevance, serving as storage compartments for hydrophobic molecules and/or catalyzing cellular signaling events at their boundaries. Furthermore, in the early stages of asymmetric enzymatic attack to the external monolayer of giant vesicles, we observe a transient coupling of the second-messenger diacylglycerol to membrane spontaneous curvature, which decreases due to enzyme activity, before domain formation and final vesicle collapse occurs.