Catalytic enantioselective 1,3-dipolar cycloaddition reactions of cyclic nitrones: a simple approach for the formation of optically active isoquinoline derivatives

The first highly diastereo- and enantioselective catalytic 1, 3-dipolar cycloaddition reaction of cyclic nitrones activated by chiral Lewis acids with electron-rich alkenes has been developed. The nitrones, mainly 3,4-dihydroisoquinoline N-oxides, are activated by chiral 3,3'-aryl BINOL-AlMe complexes and undergo a regio-, diastereo-, and enantioselective 1,3-dipolar cycloaddition reaction with especially alkyl vinyl ethers, giving the exo diastereomer of the cycloaddition products in high yield, >90% de and up to 85% ee. The reaction has been investigated under various conditions, and it is demonstrated that the reaction is an attractive synthetic procedure for the introduction of a chiral center in the 1-position of the isoquinoline skeleton. The mechanism of the reaction is discussed on the basis of the assignment of the absolute configuration of the cycloaddition product and theoretical calculations.

Catalytic enantioselective aza-Diels-alder reactions of imines--an approach to optically active nonproteinogenic alpha-amino acids

A catalytic enantioselective aza-Diels-Alder reaction of imines has been developed. The reaction of N-tosyl alpha-imino ester with different dienes including activated, non-activated, cyclic, and acyclic dienes has been investigated in the presence of various chiral Lewis acids. A series of phosphino-oxazoline ligands have been synthesized and evaluated for the reaction. It was found that the combination of phosphino-oxazoline ligands with copper(I) salts gives the best results for the activated dienes, while BINAP-copper(I) complexes are good catalysts for all the dienes studied. In the case of activated acyclic dienes the aza-Diels-Alder products can be obtained in higher than 80% isolated yield and 96% ee, while for the unactivated cyclic dienes the exo diastereomer is formed as the major product in up to 95 % ee. For an activated cyclic conjugated diene, 2-trimethylsilyloxy-1,3-cyclohexadiene, the reaction proceeds as a Mannich-type addition reaction giving optically active gamma-oxo alpha-amino acid derivatives in good yields and up to 96% ee. The reaction of an unactivated acyclic diene, 2,3-dimethyl-1,3-butadiene, with the N-tosyl alpha-imino ester gives both the aza-Diels-Alder and aza-ene products, in a ratio of 9:1 favoring the aza-Diels-Alder product. Furthermore, a series of different imines have been synthesized and investigated as possible substrates for the present catalytic enantioselective aza-Diels-Alder reaction in order to obtain mechanistic insight. All imines studied gave moderate to high ee. Particularly, the reaction of the N-phenyl and N-p-methoxyphenyl substituted glyoxylate imines with Danishefsky's diene proceeded well affording the corresponding aza-Diels-Alder product in high yield with up to 91% ee at room temperature. The present catalytic enantioselective reaction of imines provided an effective route to optically active nonproteinogenic alpha-amino acids. The products of the catalytic enantioselective aza-Diels-Alder reaction of the cyclic dienes can be used for the preparation of key compounds such as natural products and compounds of pharmaceutical interest. The absolute configurations of five products have been solved by X-ray structural analysis, and it is found that the absolute configuration of the aza-Diels-Alder adduct is dependent on the substituent on the imine nitrogen atom. It turned out that the N-tosyl glyoxylate imine and N-p-methoxyphenyl glyoxylate imine give the aza-Diels-Alder adduct with opposite absolute configuration using the same enantiomer of the catalyst. On the basis of the results the mechanistic aspects for the reactions are discussed.

Development of an unusually highly enantioselective hetero-Diels-Alder reaction of benzaldehyde with activated dienes catalyzed by hypercoordinating chiral aluminum complexes

The effect of Lewis acid catalysis of the hetero-Diels-Alder reaction between benzaldehyde and activated dienes (e.g. the Danishefsky's diene) has been investigated. In the present work we decided to study a series of chiral aluminum complexes as potential catalysts for the hetero-Diels-Alder reaction in order to gain a better understanding of the effect on the chiral induction of varying the steric and electronic environment of the metal ion. The results of this study prompted us to conclude that steric effects in the ligand coordination sphere and hypercoordination are strongly contributing factors to the optical yield of the reaction. Optimization of the reaction culminated in the synthesis of the hetero-Diels-Alder product in 99.4% ee and 97% yield of the isolated product. Based on the experimental results the mechanism for the hetero-Diels-Alder reaction is discussed and it is postulated that hypercoordination to the chiral aluminum Lewis acid center is of importance for the reaction.

Evaluation of potential closed head injury in patients with known coagulopathy

A case report is provided of an elderly "minor" trauma patient in whom an acute subdural hematoma developed. The division of traumatology and surgical critical care worked with other hospital departments to develop and implement a trauma care guideline, promote ongoing communication between departments, and monitor compliance with the guideline.

Colonization and infection with antibiotic-resistant bacteria in a long-term care facility

OBJECTIVE

To assess colonization and infection with methicillin-resistant Staphylococcus aureus (MRSA), high-level gentamicin-resistant enterococci (R-ENT) and gentamicin and/or ceftriaxone-resistant Gram-negative bacilli (R-GNB) and the factors that are associated with colonization and infection with these organisms.

DESIGN

Monthly surveillance for colonization and infection over a period of 2 years. In the second year, an intervention to decrease MRSA colonization by the use of mupirocin ointment was carried out.

SETTING

Long-term care facility attached to an acute care Veterans Affairs Medical Center.

PATIENTS

A total of 551 patients in the facility were followed for a period of 2 years.

MEASUREMENTS

Colonization and infection rates with MRSA, R-ENT, and R-GNB. Analysis of risk factors associated with colonization and infection with these three groups of organisms.

MAIN RESULTS

In the first year, colonization rates were highest for MRSA (22.7 +/- 1% patients colonized each month) and R-ENT (20.2 +/- 1%) and lower for R-GNB (12.6 +/- 1%). After introduction of decolonization of nares and wounds with mupirocin, the rate of MRSA colonization fell significantly to 11.5 +/- 1.8%, but rates remained unchanged for R-ENT and R-GNB. Risk factors for MRSA colonization included the presence of wounds and decubitus ulcers. For R-ENT, the presence of wounds, renal failure, intermittent urethral catheterization, low serum albumin, and poor functional level were significant. For R-GNB, intermittent urethral catheterization, chronic renal disease, inflammatory bowel disease, presence of wounds, and prior pneumonia were significantly associated with colonization. Overall, of infections caused by known organisms, 49.6% were due to MRSA, R-ENT, or R-GNB, and 50.4% were due to susceptible organisms. Infections were more commonly due to R-GNB (21.1% of all infections) than to R-ENT (8.3%) or MRSA (4.6%). The most common infections were urinary tract infections (42.9% of all infections) and skin and soft tissue infections (31.9% of all infections). Risk factors for MRSA infections were diabetes mellitus and peripheral vascular disease, for R-GNB infections were intermittent urethral catheterization and indwelling urethral catheters, and no one factor was associated with R-ENT infection.

CONCLUSIONS

In our long-term care facility, colonization with resistant MRSA and R-ENT was more common than R-GNB, but infections were more often due to R-GNB than R-ENT and MRSA. Several host factors, which potentially could be modified in order to prevent infections, emerged as important in colonization and infection with these antibiotic-resistant organisms.

Attempts to eradicate methicillin-resistant Staphylococcus aureus from a long-term-care facility with the use of mupirocin ointment

PURPOSE

To assess the impact of the use of mupirocin ointment on colonization, transmission, and infection with methicillin-resistant Staphylococcus aureus (MRSA) in a long-term-care facility.

PATIENTS AND METHODS

All 321 residents of a Veterans Affairs long-term-care facility from June 1990 through June 1991 were studied for MRSA colonization and infection. MRSA-colonized patients received mupirocin ointment to nares in the first 7 months and to nares and wounds in the second 5 months. The effect of mupirocin use on MRSA colonization and infection was monitored. All S. aureus strains isolated were tested for the development of resistance to mupirocin.

RESULTS

A total of 65 patients colonized with MRSA received mupirocin ointment. Mupirocin rapidly eliminated MRSA at the sites treated in most patients by the end of 1 week. Weekly maintenance mupirocin was not adequate to prevent recurrences--40% of patients had recurrence of MRSA. Overall, MRSA colonization in the facility, which was 22.7% +/- 1% prior to the use of mupirocin, did not change when mupirocin was used in nares only (22.2% +/- 2.1%), but did decrease to 11.5% +/- 1.8% when mupirocin was used in nares and wounds. Although colonization decreased, roommate-to-roommate transmission and MRSA infection rates, low to begin with, did not change when mupirocin was used. Mupirocin-resistant MRSA strains were isolated in 10.8% of patients.

CONCLUSIONS

Mupirocin ointment is effective at decreasing colonization with MRSA. However, constant surveillance was required to identify patients colonized at admission or experiencing recurrence of MRSA during maintenance treatment. Long-term use of mupirocin selected for mupirocin-resistant MRSA strains. Mupirocin should be saved for use in outbreak situations, and not used over the long term in facilities with endemic MRSA colonization.

Methicillin-resistant Staphylococcus aureus: colonization and infection in a long-term care facility

OBJECTIVE

To assess methicillin-resistant Staphylococcus aureus (MRSA) colonization, transmission, and infection over a 1-year period in a long-term care facility with endemic MRSA.

DESIGN

Monthly surveillance for MRSA colonization of nares, perineum, rectum, and wounds.

SETTING

Long-term care facility attached to an acute care Veterans Affairs medical center.

PATIENTS

All 341 patients in the facility had monthly surveillance cultures for 1 year.

OUTCOME MEASUREMENTS

Colonization and infection with MRSA.

MAIN RESULTS

The monthly MRSA colonization rate was 23% +/- 1.0%; colonization occurred most commonly in the nares and wounds. Poor functional status was associated with MRSA colonization. Most patients (65%) never acquired MRSA; 25% of patients were already colonized at admission to the facility or at the start of the study, and only 10% of newly admitted patients acquired MRSA while in the facility. These latter patients acquired several different strains in a pattern of acquisition similar to that generally seen within the facility. In the course of 1 year, only nine patients who acquired MRSA had a roommate with the same phage type; no clustering was evident, and none of these patients developed infection. Nine other patients (3%) developed MRSA infection; five of these patients required hospitalization, but none died as a result of infection.

CONCLUSIONS

In the long-term care facility in which our study took place, MRSA was endemic, and the infection rate was low. In such settings, the cost effectiveness of aggressive management of MRSA (widespread screening for MRSA and eradication with antimicrobial agents) needs to be assessed.

Emergence of nosocomial methicillin-resistant Staphylococcus aureus and therapy of colonized personnel during a hospital-wide outbreak

At the Ann Arbor Veterans Administration Medical Center, 30 patients over a 6-month period became nosocomially infected or colonized by methicillin-resistant Staphylococcus aureus. Immediate institution of strict infection control measures, in conjunction with surveillance cultures of personnel and treatment of carriers, did not limit spread of the outbreak strain of MRSA. Multiple nonoutbreak strains, phenotypically exhibiting heteroresistance, were also uncovered. Thirteen hospital personnel were identified as MRSA carriers. Trimethoprim-sulfamethoxazole (TMP-SMX) and rifampin initially eradicated the carrier state, documented by anterior nares cultures in 13 courses of treatment in 11 employees. However, three employees were recolonized, one at one month, one at both one and four months, and one at four months. Treatment of the carrier state reservoir among personnel appeared to have no effect on the emergence and spread of nosocomial MRSA.