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O Varela

Publications and source records attributed to O Varela.

At least 19 recordsLinked to original sources
PubMed1998

The glycosyl-aldonolactone approach for the synthesis of beta-D-Galf-(1-->3)-D-Manp and 3-deoxy-beta-D-xylo-hexofuranosyl-(1-->3)-D-Manp.

A convenient synthesis of free beta-D-Galf-(1-->3)-D-Manp (8a) is reported. The disaccharide is present as external unit in the lipopeptidophosphoglycan (LPPG) of Trypanosoma cruzi and internally in the lipophosphoglycan (LPG) of Leishmania. Condensation of 2,5,6-tri-O-benzoyl-D-mannono-1,4-lactone (1) with 1,2,3,5,6-penta-O-benzoyl-D-galactofuranose, promoted by SnCl4, led to the beta-glycosyl-lactone, a key intermediate for disaccharide 8a, readily obtained by successive reduction of the lactone with diisoamylborane and debenzoylation. As in the LPG of Leishmania the HO-3 group of the galactofuranose is glycosylated by alpha-D-Galp, we also synthesized 3-deoxy-beta-D-xylo-hexofuranosyl-(1-->3)-D-Manp (8b) and p-nitrophenyl 3-deoxy-beta-D-xylo-hexofuranoside for studying the influence of HO-3 in the interaction with specific glycosidases. The disaccharide 8a, and its corresponding alditol, were good substrates for the beta-D-galactofuranosidase from Penicillium fellutanum, whereas the 3-deoxyglycosides were not hydrolyzed by the enzyme.

Carbohydrate Sequence↗
PubMed1998

The response of smooth muscle cells to alpha-thrombin depends on its arterial origin: comparison among different species.

BACKGROUND: Thrombin plays a pivotal role in the pathogenesis of arterial thrombosis and exerts a wide spectrum of effects on the cells of vessel walls. METHODS: In this paper we focus on the direct role of thrombin as a mitogen for smooth muscle cells (SMCs) derived from different vessels from the vascular tree (coronary artery, aorta, carotid artery and pulmonary artery) of different species (human and pig). All cell populations examined responded mitogenically to alpha-thrombin, however the extent of this response was dependent on both vascular origin and the species from which vessels were derived. RESULTS: Thrombin (1-100 nmol L-1) induced DNA synthesis ranging from 1.5- to 4-fold baseline depending on cell type. Porcine coronary SMCs showed the highest response to thrombin (100 nmol L-1) in terms of protein and DNA synthesis (4.0 +/- 0.2-fold) and cell division (53.4 +/- 8.8%) among the tested cells. In these cells recombinant (r)-hirudin, a specific thrombin inhibitor, exhibited maximal effectiveness to block the mitogenic effect of thrombin. Human SMC response ([3H]-thymidine incorporation) to either sera or thrombin was lower than that of porcine cells. In contrast, c-fos mRNA levels induced by thrombin in human SMCs were higher than those induced in porcine cells. In human cells, thrombin elicited an overexpression of c-fos and a lower rate of [3H]-thymidine incorporation than in porcine cells. Insulin-like growth factor I but not insulin showed additive mitogenic effects with thrombin in human coronary SMCs. The response of these cells to thrombin from different sources was a function of thrombin specific activity. CONCLUSION: These results suggest that the cell system chosen to check thrombin mitogenicity not only determines thrombin quantitative effects but also may affect the effectiveness of an inhibitor to block its biological activity.

Animals↗
PubMed1997

One-pot synthesis of beta-D-Galf(1-->4)[beta-D-Galp(1-->6)]-D-GlcNAc, a 'core' trisaccharide linked O-glycosidically in glycoproteins of Trypanosoma cruzi.

Tin(IV) chloride-promoted condensation of benzyl 2-acetamido-3-O-benzoyl-2-deoxy-alpha-D-glucopyranoside (4) with penta-O-benzoyl-beta-D-galactopyranose (6) gave the derivative of beta-D-Galp-(1-->6)-alpha-D-GlcNAc 7 in 80% yield. This was glycosylated with penta-O-benzoyl-alpha, beta-D-galactofuranose (5), employing the same catalyst, to afford the protected benzyl per-O-benzoyl-beta-D-Galf(1-->4)[beta-D-Galp(1-->6)]D-GlcNAc 10 in 41% yield. Alternatively, compound 10 was obtained directly in a one-pot reaction from 4, by sequential addition of 6 and 5 (34% yield). beta-Glycosidic linkages were diastereoselectively formed. De-O-benzoylation of 10, followed by heterogeneous catalytic transfer hydrogenolysis of the benzyl group afforded the free trisaccharide beta-D-Galf(1-->4)[beta-D-Galp(1-->6)]-D-GlcNAc (14) in 98% yield from 10. Sodium borohydride reduction of 14 gave the corresponding alditol, whose spectral data were identical to those reported for the alditol obtained from the 38-43 kDa cell-surface glycoprotein of Trypanosoma cruzi.

Animals↗
PubMed1997

Monounsaturated and polyunsaturated n-6 fatty acid-enriched diets modify LDL oxidation and decrease human coronary smooth muscle cell DNA synthesis.

Proliferation of smooth muscle cells (SMCs) plays an important role in atherosclerotic lesion progression. The purpose of this investigation was to examine the effect of diets differing in fatty acid composition on human coronary SMC entry in the cell proliferation cycle. Twenty-four healthy men and women were placed on four consecutive diets lasting 5 weeks each: (1) saturated fatty acid (SFA)-rich diet with palm oil; (2) monounsaturated fatty acid (MUFA)-rich diet with olive oil; (3) polyunsaturated fatty acid (PUFA) n-6-rich diet with sunflower oil; and (4) PUFA n-3-rich diet (3.8 g/d). All diets supplied 35% of calories as fat. Compared with the SFA diet, all unsaturated diets reduced LDL cholesterol. Resistance of LDL to oxidative modification was significantly increased during the MUFA period (P < .05). Human coronary SMCs were cultured and induced by sera derived from the different groups. 3H-Thymidine incorporation into doubling DNA was significantly (P < .01) reduced during the MUFA and PUFA n-6 periods but not during the PUFA n-3 diet with respect to the SFA diet. This effect was more pronounced in women than in men. In conclusion, the MUFA-enriched diet reduced SMC DNA synthesis and LDL levels and protected LDL from oxidation. Therefore, these combined effects suggest that an oleic acid-rich Mediterranean diet could be better than PUFA (n-6)- or PUFA (n-3)-rich diets in the prevention of atherosclerosis.

Cell Division↗
PubMed1993

Synthesis and antitumor activity of anthracycline disaccharide glycosides containing daunosamine.

Daunosamine, as its 4-O-acetyl-3-N-trifluoroacetyl glycosyl chloride derivative (1b), has been coupled alpha-L-glycosidically to the 3- and 4-mono-O-acetyl derivatives of L-rhamnal to afford disaccharide glycal derivatives, whose conversion into the corresponding 2-deoxyglycosides by sequential alkoxyiodination-tributylstannane reduction has been evaluated. The sequence successfully demonstrated with the methyl glycosides was successfully extended with daunomycinone as the aglycon, providing a preparative route to 7-O-[3-O-(3-amino-2,3,6-trideoxy-alpha-L-lyxo-hexopyranosyl)- 2,6-dideoxy-alpha-L-arabino-hexopyranosyl]daunomycinone hydrochloride (15), an analogue of natural anthracycline antibiotics containing daunosamine and a 2,6-dideoxy-L-hexose.

Aminoglycosides↗
PubMed1990

Convenient syntheses of 5-O- and 3,5-di-O-(beta-D-galactofuranosyl)-D-galactofuranose.

Benzoylation of D-galactono-1,4-lactone with 2.2 mol of benzoyl chloride, at -23 degrees, gave the 2,6-dibenzoate (2, 62%). Tin(IV) chloride-catalyzed glycosylation of 2 with 1,2,3,5,6-penta-O-benzoyl-alpha,beta-D-galactofuranose (1) afforded 2,6-di-O-benzoyl-5-O-(2,3,5,6-tetra-O-benzoyl-beta-D-galactofuranosyl)-D - galactono-1,4-lactone (4, 70%), HO-3 of which was benzoylated to give 5. The structure of 4 was confirmed by its conversion into crystalline beta-D-Galf-(1----5)-D-Gal-ol (8). Reduction of the lactone function of 5 with di-isoamylborane followed by debenzoylation gave beta-D-Galf-(1----5)-D-Galf (7). A by-product of the condensation of 1 with 2 was characterized as 2,6-di-O-benzoyl-3,5-di-O-(2,3,5,6-tetra-O-benzoyl-beta-D-galactofuranos yl)-D- galactono-1,4-lactone (9), which was converted, as for 5, into beta-D-Galf-(1----3)[beta-D-Galf-(1----5)]-D-Galf (13).

Carbohydrate Sequence↗
PubMed1989

Confirmation of the structures of the products obtained on acylation of 2-amino-2-deoxy-D-gluconic acid.

Acetylation of 2-amino-2-deoxy-D-gluconic acid (1) with acetyl chloride-pyridine gave 2,3-unsaturated six- and five-membered lactones (2 and 3). Their benzoylated analogs (4 and 5) were obtained by benzoylation of 1 with benzoyl chloride-pyridine. Reaction of 1 with hot acetic anhydride-sodium acetate gave a approximately 1:2 mixture of (E)- and (Z)-2-acetamido-6-acetoxyhexa-2,4-dien-4-olide (6-E and 6-Z). Treatment of 3 with 1,8-diazabicyclo[5.4.0]undec-7-ene also gave as the main product 6-Z, which was isolated crystalline from the reaction mixture. The same reaction applied to compound 5 gave selectively the Z-isomer of the benzoylated furanone 7. Partial and total hydrogenation (H2-Pd-C) of the mixture 6-E, Z gave, respectively, a racemic monounsaturated lactone (8) and a dideoxy lactone (9), for which the threo-configuration for the chiral centers at C-2 and C-4 was determined. Acidic removal of the acetyl groups from 9 afforded the 2-amino-6-hydroxy-1,4-lactone hydrochloride 10. On the other hand, acetylation at high temperature of the 4,6-O-benzylidene derivative of 1 (11) gave the 2,3-unsaturated, six-membered lactone (12), precursor of 2-acetamido-6-acetoxyhexa-2,4-dien-5-olide (14).

Acetylation↗
PubMed1989

Synthesis of galactofuranose disaccharides of biological significance.

Methyl beta-D-galactofuranoside was readily obtained by tin(IV) chloride-catalyzed glycosylation of penta-O-benzoyl-alpha,beta-D-galactofuranose, followed by debenzoylation with sodium methoxide. Glycosylation of 1 with 2,3,5-tri-O-benzoyl-D-galactono-1,4-lactone or with the 6-O-trityl-lactone derivative 5 gave the benzoylated beta-D-galactofuranosyl-(1----6)-D-galactono-1,4-lactone 6 in excellent yield. The structure of disaccharide 6 was confirmed by borohydride reduction to the glycosyl-alditol 7. A byproduct of the condensation reaction of 1 with 4 or 5 was identified as the benzoylated (1----1)-beta,beta'-D-galactofuranosyl disaccharide 8. Compound 8 was readily prepared (88% yield) by controlled addition of water to 1, in the presence of stannic chloride. O-Debenzoylation of 8 afforded crystalline beta'-D-galactofuranosyl-(1----1)-beta-D-galactofuranoside. The glycosyl-lactone 6 constitutes a key intermediate for the synthesis of a disaccharide derivative having both units in the furanoid form. Thus, diisoamylborane reduction of the lactone function of 6 led to the disaccharide derivative 10, from which the methyl glycoside 12 was prepared. O-Debenzoylation of 12 gave the corresponding methyl beta-D-galactofuranosyl-(1----6)-beta-D-galactofuranoside. The free disaccharide beta-D-Galf-(1----6)-D-Galp and its acetylated derivative were also synthesized from 10.

Carbohydrate Conformation↗
PubMed1985

Synthesis and antitumor activity of 2'-bromo- and 2'-chloro-3'-acetoxy-3'-deaminodaunorubicin analogs.

Bromination of 3,4-di-O-acetyl-L-rhamnal (7) and subsequent glycosidic coupling under Koenigs-Knorr conditions with daunomycinone gave a mixture of three compounds having the beta-L-gluco (10), alpha-L-gluco (11), and alpha-L-manno (12) configurations. Analogous bromination of 3,4-di-O-acetyl-L-fucal (13) followed by coupling with daunomycinone gave a mixture of three glycosides having the beta-L-galacto (16), alpha-L-galacto (17), and alpha-L-talo (18) configurations. Chlorination of 7 and coupling with daunomycinone in the presence of silver triflate gave products having the alpha-L-gluco (21) and alpha-L-manno (22) configurations, whereas 13, under similar conditions, gave only one stereoisomeric product, that having the alpha-L-galacto (24) configuration. Compounds 12 and 22 showed high in vivo activity in the P-388 lymphocytic leukemia assay.

Animals↗
PubMed1985

Selective acylation of 6-deoxyglycals.

L-Rhamnal was acylated under a variety of conditions with various acylating reagents. Substitution of the hydroxyl group in the allylic position was favored when acetyl chloride, N-acetylimidazole, benzoyl chloride, and N-benzoylimidazole were used (40-60% net yields), whereas the homoallylic group of L-rhamnal was selectively protected when acetic anhydride-pyridine was employed for the acylation. The monoacetates of L-fucal underwent O-3----O-4 migration of the acetyl group, and selective acylation of this glycal could not be achieved.

Acylation↗
PubMed1984

Crystalline 2,3:4,5-di-O-isopropylidene-DL-arabinose diethyl dithioacetal: some reactions of acetal derivatives of arabinose.

Acetonation of the diethyl dithioacetals of D- and L-arabinose gives the corresponding 2,3:4,5-diisopropylidene acetals (2a and 2b) as oils having [alpha]D +82 and -81 degrees, respectively; in admixture, the enantiomers form a well crystallized racemate, m.p. 43-45 degrees. The initial product of acetonation is the 4,5-monoisopropylidene acetal. Demercaptalation of 2a with mercury(II) chloride-cadmium carbonate gives 2,3:4,5-di-O-isopropylidene-aldehydo-D-arabinose (5) in high yield, but the literature procedure employing mercury(II) chloride-mercury(II) oxide affords a mixture of 5 and 1,2:3,4-di-O-isopropylidene-beta-D-arabinopyranose (6). A trace of acid readily and completely converts the aldehydo derivative 5 into the cyclic diacetal 6.

Acetals↗
PubMed1984

3'-Deamino-4'-epi-3'-hydroxy-daunorubicin and -doxorubicin. Synthesis and antitumor activity.

3'-Deamino-4'-epi-3'-hydroxy-daunorubicin (11) and -doxorubicin (14) have been synthesized. In the in vivo murine P-388 lymphocytic leukemia assay, these two compounds were more active than daunorubicin (1) and doxorubicin (2), respectively. Comparative studies in the P-388 assay indicated 3'-deamino-3'-hydroxydoxorubicin (3) to be more active than its 4'-epimer 14.

Animals↗
PubMed1984

Synthesis and antitumor activity of 3'-deamino-3'-hydroxydoxorubicin. A facile procedure for the preparation of doxorubicin analogs.

Two successful routes have been developed for preparation of 3'-deamino-3'-hydroxydoxorubicin (11), based on protection of the 14-hydroxyl group of the aglycon by using tert-butylchlorodimethylsilane. The key intermediate, 14-O-tert-butyldimethylsilyl-7-O-(3,4-di-O-acetyl-2,6-dideoxy-alpha-L-ly xo -hexopyranosyl)adriamycinone (9), was successively deacetylated and desilylated in high yield to give the desired product 11. This route constitutes a general method of access to glycon-modified doxorubicin analogs. Compound 11 showed high antitumor activity in vivo in the murine P388 lymphocytic leukemia assay.

Animals↗
PubMed1980

[Transparieto-hepatic cholangiography with Chiba needle].

253 percutaneous transhepatic cholangiographies with Chiba needle were performed. In 83% of the cases the biliary tract could be visualized. In the patients with extrahepatic cholestasis 92% success was achieved, while only 48% success in the cases with intra-hepatic cholestasis. Complications were developed in 3,87% of cases (choleperitoneum 4, cholangitis 2, hemorrhage 2, paralytic ileum 1, hemobilia 2). There was no mortality. Patients with dilated biliary tract should be operated upon in no more than 24 hours following the procedure.

Adolescent↗