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J Balsells

Publications and source records attributed to J Balsells.

At least 19 recordsLinked to original sources
PubMed2001

Achiral tetrahydrosalen ligands for the synthesis of C(2)-symmetric titanium complexes: a structure and diastereoselectivity study.

Achiral tetrahydrosalen ligands have been employed in the synthesis of chiral C(2)-symmetric titanium complexes. When combined with tetrahydrosalen ligands 2a and 2b, titanium tetraisopropoxide liberated 2 equiv of isopropyl alcohol and generated the (tetrahydrosalen)Ti(O-i-Pr)(2) complexes 3a and 3b. These complexes were shown to be C(2)-symmetric by (1)H and (13)C[(1)H] NMR spectrometry and X-ray crystallography. X-ray structures of 3a and 3b indicate that the bonding of the tetrahydrosalen ligand to titanium is different than the bonding of salen ligands to titanium. Whereas salen ligands usually bind to titanium in a planar arrangement, the tetrahydrosalen is bonded with the phenoxide oxygens mutually trans. When bound in this fashion, the nitrogens of the tetrahydrosalen ligand and the titanium become stereogenic centers. The use of titanium complexes of high enantiopurity in the generation of tetrahydrosalen titanium adducts resulted in a maximum diastereoselectivity of 2:1. The diastereoselectivity obtained using chiral titanium alkoxide complexes was greater than the diastereoselectivity observed when a tetrahydrosalen ligand derived from (S,S)-trans-diaminocyclohexane was employed.

Journal Article↗
PubMed2001

Toward the total synthesis of variecolin.

[reaction: see text] An annulative approach toward the total synthesis of the sesterterpenoid variecolin (1) is presented. Synthesis of the key hemiketal, containing the core ABC ring skeleton, has been achieved on a model system by an expeditious route utilizing samarium(II) iodide. Furthermore, enantioselective syntheses of component fragments for the total synthesis have been developed.

Angiotensin Receptor Antagonists↗
PubMed2001

Optimization of asymmetric catalysts using achiral ligands: metal geometry-induced ligand asymmetry.

[reaction: see text] Traditionally, asymmetric catalysts have been optimized by modification of resolved chiral ligands. In this Letter, we optimize the asymmetric addition of diethylzinc to aldehydes by modification of achiral methylene bis(phenol) ligands. Upon coordination of the substrate, the achiral ligand becomes asymmetric, a concept termed Metal Geometry-Induced Ligand Asymmetry. The enantioselectivity of the catalyst formed from a single resolved ligand and several achiral ligands ranged from 9% (R) to 83% (S).

Aldehydes↗
PubMed2001

Snapshots of titanium BINOLate complexes with diverse solid state structures.

[structure: see text]. Many important asymmetric reactions are catalyzed by (BINOLate)Ti species with unknown structures. Reported here are three structures of BINOLate titanium complexes that show an interesting aggregation of (BINOLate)Ti(OiPr)2 with itself and with titanium tetraisopropoxide. These complexes are potential intermediates in the asymmetric addition of alkyl groups to aldehydes.

Journal Article↗
PubMed2000

Low-energy pathway for pauson-khand reactions: synthesis and reactivity of dicobalt hexacarbonyl complexes of chiral ynamines

A family of dicobalt hexacarbonyl complexes of 1-(dialkylamino)-2-(trimethysilyl)acetylenes (3a-f) derived both from achiral and chiral amines [a, morpholine; b, (S)-2-methoxymethylpyrrolidine; c, (2R,5R)-2, 5-bis(methoxymethyl)pyrrolidine; d, (+/-)-trans-2, 5-bis(benzyloxymethyl)pyrrolidine; e, (2R,5R)-2, 5-dimethylpyrrolidine; f, (S)-(alpha-methylbenzyl)benzylamine] has been prepared by a one-stage process from dichloroacetylene. The methanolysis at room temperature of these complexes (MeOH/K(2)CO(3)) induces the selective cleavage of the carbon-silicon bond, leading to the thermally unstable terminal ynamine complexes 12a-f. The Pauson-Khand reaction of 12a-f with strained olefins (norbornadiene and norbornene) takes place at unprecedentedly low temperatures (-35 degrees C) in the absence of chemical promoters. Diastereoselectivities of up to 94:6 are recorded in these reactions with the ynamine complexes derived from C(2) symmetrical chiral auxiliaries (12c,d). The high reactivity depicted by terminal ynamines in the Pauson-Khand reaction has been analyzed by theoretical semiempirical procedures [PM3(tm)] and with density functional theory (VWN/B88), and appears to reflect an easy CO loss from the ynamine-dicobalt hexacarbonyl complexes.

Journal Article↗
PubMed2000

[Cerebrovascular accident as the form of presentation of a pancreatic cystadenocarcinoma: an unusual form of presentation in a rare tumor].

Pancreatic cystadenocarcinoma is an uncommon neoplasm of the pancreas. Mucinous cystadenocarcinoma is the most frequent pancreatic cystadenocarcinoma. Symptoms are often non-specific but abdominal pain and jaundice are common in tumors localized in the head of the pancreas. Thromboembolic manifestations of pancreatic neoplasm have been described but are infrequent. The commonest manifestations are migratory thrombophlebitis, mesenteric venous thrombosis and pulmonary embolism. Cerebral stroke as the first manifestation of pancreatic carcinoma is exceptional. The mechanism by which pancreatic carcinoma induces stroke is unclear, although Trousseau's syndrome, complications of mucinous cancer or blood disorders could play a role. We report the case of a young woman with transient stroke and paraneoplastic thrombocytosis in whom pancreatic cystadenocarcinoma was diagnosed.

Adult↗
PubMed1998

Cross-clamping of the three hepatic veins in the piggyback technique is a safe and well tolerated procedure.

A common stump of the three hepatic veins has always been used to fashion the upper vena cava anastomosis in 205 liver transplantations with the piggyback (PGB) technique performed in our Unit, to avoid outflow problems. The aim was to study the repercussion of lateral inferior vena cava (IVC) clamping on IVC flow and pressure as well as on systemic hemodynamics. We have studied 42 orthotopic liver transplantations performed with the PGB technique. Intraoperative IVC blood flow measurements by transit time ultrasonic volume flowmetry, IVC pressure, and systemic hemodynamics were taken before and after lateral IVC clamping. Graft outflow complications, stenosis or kinking of the upper vena cava anastomosis have not been found in any of the 205 PGB procedures. A significant decrease of IVC flow (23%) and cardiac output (12%) occurred after IVC clamping, whereas mean arterial and central venous pressures were not altered significantly, probably due to an increase (25%) of systemic vascular resistance. Only in one case was an almost total clamping of IVC needed. Venovenous bypass was not needed in any case. Renal perfusion pressure was adequate in all cases. We conclude that the use of a common stump of the three hepatic veins for upper vena cava anastomosis in the PGB technique is safe because any outflow problem of the graft is avoided and, at the same time, is well tolerated hemodynamically because most of the IVC flow is preserved.

Constriction↗
PubMed1998

Biliary complications secondary to late hepatic artery thrombosis in adult liver transplant patients.

Biliary complications (BC) are the usual presentation of late hepatic artery thrombosis (HAT) of the liver graft. Our aim was to study the clinical features and outcome of BC secondary to HAT compared to BC which occurred in liver transplant (LT) patients with patent vessels. We present a retrospective study of 224 LTs performed in 204 patients between 1988 and 1996. The mean recipient x s age was 51 years. A choledochocholedochostomy without T-tube was used as biliary reconstruction in most cases (67%); in 12%, a choledochojejunostomy was performed. An iliac conduit was necessary in 15% of cases and back-table arterial reconstruction was performed in 10% of cases of anatomic variants in graft arteries. Different donor, recipient and intraoperative variables, as well as treatment and outcome. were studied in the two groups of patients presenting BC with or without HAT. BC occurred in 38 cases (17%) whereas HAT was diagnosed in 11 cases (4.9%). Therefore, 23% of BC encountered after LT were secondary to HAT. Nine cases of late HAT manifested as BC, septicaemia (88%) and hepatic bilomas (8 cases). Percutaneous or surgical drainage of hepatic bilomas was performed in all cases, followed by retransplantation in six cases (66%). BC secondary to HAT appeared later than the rest of BC. Donor age was the only significant predisposing factor found in our study. Graft survival is significantly reduced as most patients needed retransplantation. In conclusion, BC secondary to HAT presented later in livers from older donors in the form of biliary sepsis and hepatic biloma. Retransplantation was ultimately required in most cases and graft survival was significantly diminished.

Bile Duct Diseases↗
PubMed1998

Early use of tacrolimus as rescue therapy for refractory liver allograft rejection.

The aim of this study was to compare two different periods of tacrolimus rescue therapy for intractable rejection. From January 1992 to May 1996, 140 liver transplants (LTx) were performed in our hospital under cyclosporine A-based immunosuppression. Twenty-four (17.1%) patients were switched to tacrolimus because of chronic rejection, steroid-resistant rejection or cholestasic hepatitis C recurrence. Mean follow-up was 21 months (range 12-56 months). In the first period (January 1992-March 1994), conversion to tacrolimus was indicated later, after unsuccessful repeated rejection therapy. In the second period (April 1994-May 1996), conversion to tacrolimus was indicated early, immediately after unsuccessful rejection therapy or directly at the moment of diagnosis with no further treatment. Eleven of 54 LTx were treated with tacrolimus in period 1 (20.3%), and 13 of 86 LTx in period 2 (15.1%). Only 4 of 11 (36.6%) grafts converted were rescued during the first period, while 11 of 13 (84.6%) were rescued in the second (P < 0.03). Patients in the first period received more courses of steroids than those of the second (1.7 +/- 0.7 vs 0.9 +/- 0.7, P < 0.02). Furthermore, six patients received one or two courses of OKT3 in period 1 while only one received one course in period 2 (P < 0.03). Preconversion mean bilirubin levels of patients in the first period were higher than those in the second (15.9 +/- 7.3 mg/dl vs 9.7 +/- 5.8 mg/dl, P < 0.05). Preconversion mean bilirubin levels of 6.8 +/- 5.4 mg/dl and 21.8 +/- 18.5 mg/dl were observed in patients with successful and unsuccessful tacrolimus rescue therapy, respectively, independent of the treatment period (P < 0.05). Mortality rates were higher in the first period than in the second (82% versus 23%; P < 0.02). In conclusion, conversion to tacrolimus as rescue therapy for intractable rejection or cholestasic hepatitis C recurrence is an efficacious alternative, particularly when tacrolimus is initiated early.

Graft Rejection↗
PubMed1998

Risk factors for acute renal failure requiring dialysis after liver transplantation.

Acute renal failure (ARF) is a common and severe complication after liver transplantation (LT). The aim of this study was to ascertain the impact of ARF requiring dialysis in the outcome of LT and to analyze the risk factors leading to this event in the early post-operative period. From October 1988 to December 1994, 172 LT were performed in 158 patients. Postoperative ARF occurred in 88 transplants (51.1%) during the early postoperative period: mild ARF was found in 46 (serum creatinine 1.5-3 mg/dl), moderate ARF in 12 (serum creatinine > 3 mg/dl) and severe ARF in 30 (serum creatinine > 3 mg/dl with dialysis requirement). Preoperative, intraoperative, and postoperative variables were studied, comparing patients presenting severe ARF with the remaining patients. Postoperative mortality in the dialysed group was much higher than in the non-dialysis group (50% vs. 13.4%)(p < 0.001) and 1-yr actuarial graft survival was 73.4% for the non-dialysed group compared with 40.9% for the dialysed group (p < 0.05). Among 38 variables investigated, only two factors had independent prognostic value in multivariate analysis: preoperative serum creatinine > 1.5 mg/dl (OR = 4.4, p = 0.006) and graft dysfunction grades III-IV (OR = 8.9, p = 0.001). In conclusion, ARF is a severe complication post-LT; its appearance could be predicted in patients with pre-transplant renal dysfunction, severe graft dysfunction, or both. However, in many cases renal function may revert to normal if treated aggressively with early dialysis support.

Acute Kidney Injury↗
PubMed1996

Resection of hepatocellular carcinoma in patients with cirrhosis.

Between 1987 and 1993, 53 hepatic resections for hepatocellular carcinoma (HCC) were performed in 51 patients with cirrhosis. Limited hepatic resection was performed in 66 per cent of patients. The postoperative mortality rate was 13 per cent. The tumours recurred in 27 patients (53 per cent), and the cumulative recurrence rate at 1 and 4 years was 41 and 89 per cent, respectively. Mean time to recurrence was 11.7 months and the most frequent site was the liver (21 patients). The only significant risk factor for recurrence was symptomatic tumours. The recurrence rate of HCC in patients with cirrhosis with surgical resection alone is high and actuarial survival at 4 years is very low. Other approaches to the treatment of HCC in patients with cirrhosis require consideration.

Adult↗
PubMed1996

Is hepatitis C virus recurrence a risk factor for chronic liver allograft rejection?

Several risk factors have been reported that may favour the development of chronic rejection. From October 1988 to December 1993, 97 liver transplants with survival of more than 3 months were included in the study. Fifty-two patients (54.1%) had chronic hepatitis C virus (HCV) infection before liver transplantation. Immunosuppression consisted of cyclosporine A and prednisone, whereas 14 patients received FK 506 and prednisone. Severe graft HCV reinfection was present in 32 patients (61.5%) after liver transplantation and chronic graft hepatitis C was found in 26 cases at the end of the study. Chronic rejection occurred in 8 of 97 allografts (8.25%); 5 presented chronic rejection and concomitant chronic graft hepatitis C. The incidence of chronic rejection in patients with HCV infection before liver transplantation (9.6%) did not differ when compared with the negative HCV patients (6.6%). However, when the 26 cases that developed graft dysfunction due to chronic hepatitis C after liver transplantation were considered, 5 presented chronic rejection, a significantly higher incidence than in the remaining patients (3 of 71) (Yates chi-square test: P < 0.05). In our experience, there appears to be a relationship between the development of chronic rejection and chronic hepatitis C in the graft after liver transplantation.

Graft Rejection↗
PubMed1996

Influence of anti-HLA antibodies and positive T-lymphocytotoxic crossmatch on survival and graft rejection in human liver transplantation.

BACKGROUND/AIMS: The role of crossmatching in liver transplantation is controversial. The aim of this study was to investigate retrospectively the effect of sensitization and IgG lymphocytotoxic crossmatching on liver transplantation. METHODS/RESULTS: Over 5 years, 20 of 243 (8.2%) first liver transplants were performed with a positive crossmatch and their outcome was compared with the remaining 223 performed with a negative crossmatch. Women had a higher incidence of positive crossmatch than men (p < 0.001). Significant differences in mean panel reactive antibody of 2.7% and 43.3% were found in negative and positive crossmatch patients, respectively (p < 0.001). Severe early rejection resulting in graft loss occurred in eight of 20 positive crossmatch patients, and only one of 223 negative crossmatch patients (p < 0.001). Five of the remaining positive crossmatch patients suffered several acute rejection episodes some months after liver transplantation. Two of 20 in the positive crossmatch group developed chronic rejection (10%) compared with ten of 223 negatives (4.4%) (N.S). Nine of 16 positive crossmatch female recipients suffered graft loss and seven died, representing 1-year graft and patient survival of 56% and 43%, respectively. Fifteen of 68 negative crossmatch female recipients presented graft loss and 12 died, accounting for 1-year patient and graft survival of 82% and 78% (p < 0.005), respectively. Five patients (20%) displayed positive crossmatch at the time of retransplantation, compared with 24 (10%) who were negative (N.S). CONCLUSION: Our experience confirms the adverse impact of a positive crossmatch in liver transplantation, particularly in female recipients. Candidates with high panel reactive antibody are more likely to display a positive crossmatch, and therefore to develop early severe rejection and graft failure.

Adult↗
PubMed1996

DNA ploidy study of resected hepatocellular carcinoma in cirrhotic liver.

BACKGROUND/AIMS: Results of several studies on DNA ploidy as a prognostic indicator in hepatocellular carcinoma are contradictory. The present study analysed the correlations between DNA ploidy of resected hepatocellular carcinoma and tumour characteristics, tumour recurrence, risk factors and survival. METHODS: Tumoural DNA ploidy of hepatocellular carcinomas from 37 patients with cirrhosis who underwent curative tumour resection was studied by flow cytometry. RESULTS: A diploid pattern was found in 23 hepatocellular carcinomas (62.2%) and an aneuploid pattern in 14 (37.8%). The tumour recurrence rate did not differ statistically between diploid (69.6%) and aneuploid (50%) hepatocellular carcinomas. The only prognostic variable with significant difference in DNA pattern was the histologic tumour type; the majority of non-trabecular tumours were aneuploid while most trabecular hepatocellular carcinomas had a diploid DNA pattern. Actuarial survival at 1, 2, 3 and 4 years of patients with diploid and aneuploid tumours was 69.6%, 40.6%, 16.2% and 0%, and 69.3%, 59.4%, 49.5% and 32.9%, respectively (log rank p = 0.1927). CONCLUSION: These results indicate that DNA ploidy has no prognostic value in hepatocellular carcinoma.

Adult↗