Bioorganometallic chemistry. 13. Regioselective reduction of NAD(+) models, 1-benzylnicotinamde triflate and beta-nicotinamide ribose-5'-methyl phosphate, with in situ generated [CpRh(Bpy)H](+): structure-activity relationships, kinetics, and mechanistic aspects in the formation of the 1,4-NADH derivatives.

Cofactor regeneration; i.e., regiospecific conversion of NAD(+) to 1,4-NADH, has been extensively studied and is a crucial component in the eventual use of 1,4-NADH in a variety of bioorganic synthesis processes involving the formation of chiral organic compounds. We have studied the reduction of a model NAD(+) compound, 1-benzylnicotinamide triflate, 1a, using [CpRh(bpy)(H(2)O)](2+), 2 (Cp = eta(5)-C(5)Me(5), bpy = 2,2'-bipyridyl), as the catalyst precursor and sodium formate (HCO(2)Na) as the hydride source in 1:1 H(2)O/THF and have found exclusive 1-benzyl-1,4-dihydronicotinamide regioselectivity, as was observed previously for natural NAD(+) that provided 1,4-NADH (see: Steckhan et al. Organometallics 1991, 10, 1568). Moreover, a variety of 3-substituted derivatives of 1-benzylpyridinium triflate, in addition to the -C(O)NH(2) group (1a), were also studied to ascertain that this 3-functionality (e.g., -C(O)NHCH(3), -C(S)NH(2), -C(O)CH(3), -C(O)OCH(3), and -CN, 1b,d-g) coordinates to a [CpRh(bpy)H](+) complex to direct the concerted, regioselective transfer of the hydride group from the rhodium to the 4-ring position of the NAD(+) model; all coordinating 3-substituents had relative rates in the 0.9-1.3 range with substrate 1a set to 1.0. If in fact the 3-substituent presented a steric effect [-C(O)NH(CH(2)CH(3))(2), 1c] or was a nonbinding group (-CH(3), 1h; -H, 1i), no catalytic hydride transfer was observed even with the more electrophilic 2 and 6 ring positions being readily available, which further implicated the crucial coordination of the NAD(+) model to the CpRh metal ion center. We also found that the 1-benzyl substituent on the nitrogen atom exerted a substantial electron-withdrawing effect, in comparison to the electron-donating 1-methyl substituent, and favorably affected the rate of the regioselective reduction (rate enhancement of 1-benzyl/1-methyl = 2.0). The kinetics of the regioselective reduction of 1a were studied to show that the initial rate of reduction, r(i), is affected by the concentrations of the substrate, 1a, precatalyst, 2, and the hydride source, HCO(2)Na, in 1:1 H(2)O/THF: d[1-benzyl-1,4-dihydronicotnamide]/dt = k(cat)[1a][2][HCO(2)Na]. Furthermore, we wish to demonstrate that a previously synthesized aqueous NAD(+) model, beta-nicotinamide ribose-5'-methyl phosphate, 3, shows a similar regioselectivity for the 1,4-NADH analogue, while the initial rate (r(i)) for the regioselective reduction of 3 and NAD(+) itself was found to be comparable in water but faster by a factor of approximately 3 in comparison to 1a in 1:1 H(2)O/THF; the solvent, THF, appeared to inhibit the rate of reduction in 1a by presumably competing with the substrate 1a for the CpRh metal ion center. However, in H(2)O, the initial kinetic rate for substrate 3 was not affected by its concentration and implies that, in H(2)O, [CpRh(bpy)H](+) formation is rate determining. We assume that binding of 3 and NAD(+) to the CpRh metal ion center is also a pertinent step for 1,4-dihydro product formation, the experimental rate expression in H(2)O being d[1,4-dihydro-beta-nicotinamide ribose-5'-methyl phosphate]/dt = k(cat)[2][HCO(2)Na]. What we have discovered, for the first time, is evidence that the regioselective reduction of NAD(+) to 1,4-NADH by [CpRh(bpy)H](+) is a consequence of the amide's ability to coordinate to the CpRh metal center, thereby constricting the kinetically favorable six-membered ring transition state for plausible concerted hydride transfer/insertion to C4 to regioselectively provide the 1,4-NADH derivative; [CpRh(bpy)H](+) can be categorized as a biomimetic enzymatic hydride via its ability to bind and regioselectively transfer hydride to C4, exclusively. Clearly, the pyrophosphate and adenosine groups associated with the structure of NAD(+) are not essential in the rate of hydride transfer to C4, with NAD(+) model 3 having a similar initial rate (r(i)) of reduction as NAD(+) itself in water. Finally, a catalytic cycle will be proposed to account for our overall observations.

Toxoplasmosis neuroretinitis.

BACKGROUND: Neuroretinitis is a distinct clinical entity consisting of moderate to severe visual loss, optic nerve head edema, macular exudate in a stellate pattern, and variable vitreous inflammation. Although the etiology is usually postviral or idiopathic, an acute infectious cause occasionally is demonstrated. METHODS: Five juvenile or young adult patients with neuroretinitis are presented with serologic evidence of Toxoplasma gondii infection. Four of the five patients were treated with systemic antibiotics and corticosteroids; one patient was not treated. RESULTS: With a mean follow-up period of 50 months, visual acuity returned to 20/25 or better in four patients, with one patient regaining visual acuity of 20/60. Two patients had one or more recurrent episodes of neuroretinitis, distinguishing toxoplasmosis from idiopathic neuroretinitis, which is usually a monophasic illness. CONCLUSION: Toxoplasmosis infection is a rare, but potentially treatable, form of neuroretinitis and should be included in the differential diagnosis of "Leber's idiopathic stellate retinopathy."

Pathology of cytomegalovirus retinitis treated with sustained release intravitreal ganciclovir.

BACKGROUND: An experimental sustained release intraocular device has been designed to deliver ganciclovir over a long period of time. As part of an efficacy trial, the ganciclovir intraocular device was used to treat cytomegalovirus (CMV) retinitis in patients with acquired immune deficiency syndrome (AIDS). METHODS: All patients had active CMV retinitis that had progressed despite intravenous ganciclovir therapy. The ganciclovir intraocular device was inserted into the vitreous cavity by making an inferotemporal full-thickness circumferential sclerotomy and anchored to the incision. Intravenous therapy was then discontinued and patients were followed up at 2-week intervals until death. Seven eyes from five patients were obtained 2 to 10 hours postmortem and submitted for histopathologic examination. Light and electron microscopic studies were performed and correlated to the clinical outcome. Follow-up period after device placement ranged from 16 to 82 days (median, 70 days). RESULTS: All seven eyes showed clinical stabilization of the CMV retinitis. Light microscopy showed varying degrees of retinal atrophy with areas of gliosis. In addition, we observed syncytial megalic cells containing Cowdrey type A inclusions affecting all layers of the retina. Concurrent choroidal infections with Pneumocystis carinii (1) and Mycobacterium avium (2) also were seen. Electron microscopy showed virus particles located mostly at the junction of uninvolved and "healed" retinitis. No evidence of retinal toxic effects or inflammation at the site of ganciclovir intraocular device implant was noted. CONCLUSION: The ganciclovir intraocular device appeared to be effective in controlling the progression of CMV retinitis. The clinical and pathologic results are similar to those observed in the eyes of patients with intravenously administered ganciclovir. The lack of toxic effects and sustained levels of intravitreal ganciclovir may provide an improved therapeutic method of local treatment of CMV retinitis.

Control of cytomegalovirus retinitis using sustained release of intraocular ganciclovir.

An experimental intravitreal sustained-release device containing ganciclovir was used to treat 22 patients with acquired immunodeficiency syndrome-associated cytomegalovirus retinitis. Fourteen eyes were excluded (five not involved and nine with macular scarring and/or severe debility). Thirty eyes received the ganciclovir intraocular device implant and were prospectively followed up from 16 to 419 days (median, 125 days). Twenty-seven (90%) of 30 eyes showed stabilization of the retinitis. Nine (33%) of 27 eyes showed reactivation of the retinitis once the device was empty of ganciclovir; seven received a replacement device, with subsequent stabilization of the retinitis. Postoperative complications included vitreous hemorrhage (n = 1), endophthalmitis (n = 1), and progressive retinitis (n = 2). Late retinal detachment was seen in three eyes (11%) at 35 to 140 days. Survival analysis of all 30 eyes revealed the mean time to progression of retinitis to be 19 weeks (133 days). The ganciclovir intraocular device offers a promising alternative for the treatment of cytomegalovirus retinitis associated with acquired immunodeficiency syndrome.

Pseudohypopyon in unilateral acute idiopathic maculopathy.

Unilateral acute idiopathic maculopathy (UAIM) is a recently described condition in young adults consisting of rapidly progressive central visual loss, gray-white opacification of the outer retina, and serous detachment of the macula. Bull's eye pattern pigmentary changes may occur in the macula after resolution of the acute phase of the disease. A case of UAIM in which a shifting of subretinal inflammatory infiltrate was observed is reported. This is the tenth reported case of UAIM, and represents a variation in the clinical presentation of this disease. The appearance and the shifting of the subretinal infiltrate seen in this patient support an inflammatory etiology of UAIM.

Macular pseudoholes. Clinical features and accuracy of diagnosis.

BACKGROUND: Epimacular membrane with pseudohole is an important vitreomacular disorder that belongs in the differential diagnosis of impending and established macular hole. To better characterize this lesion, the authors attempted to identify various features of eyes with epimacular membrane and pseudohole. METHODS: Demographic, clinical, photographic, and fluorescein angiographic data for 14 eyes with epimacular membrane and pseudohole were reviewed. Horizontal and vertical diameters of the pseudoholes were measured, and the original diagnosis was recorded for each eye. Fluorescein angiography was performed in 11 eyes. RESULTS: The mean age of patients with macular pseudoholes was 61.6 years, and median visual acuity for pseudohole eyes was 20/30. Mean horizontal and vertical diameters of the pseudoholes were 384 and 410 microns, respectively. None of the eyes with pseudoholes had the characteristic ophthalmoscopic features associated with full-thickness macular holes or impending macular holes. Results of fluorescein angiography showed three eyes with increased tortuosity or abnormal straightening of the perifoveal vessels; three eyes with a foveal window defect; and three eyes with late leakage from the perifoveal vessels. The original diagnosis of the initial examining physician was correct in only 43% of eyes with epimacular membrane and pseudohole. CONCLUSION: Epimacular membrane with pseudohole may be an underdiagnosed lesion and commonly mistaken for impending macular hole, full-thickness hole, or lamellar hole. These data may be of use as more patients are being considered for recently advocated surgical treatments for impending and established macular hole.

Retinal periphlebitis in patients with acquired immunodeficiency syndrome with cytomegalovirus retinitis mimics acute frosted retinal periphlebitis.

Acute frosted retinal periphlebitis is an inflammatory condition of unknown origin characterized by marked perivenular infiltration in otherwise healthy patients. We encountered seven patients with acquired immunodeficiency syndrome who exhibited visual loss associated with an unusual diffuse retinal periphlebitis very similar in appearance to acute frosted retinal periphlebitis. Each patient developed a thick inflammatory infiltrate surrounding the retinal venules, creating a frosted appearance. Two cases were bilateral. All patients had areas of more typical cytomegalovirus retinitis in their involved eye(s). Five of six patients treated with ganciclovir sodium showed improvement not only of the cytomegalovirus retinitis but also of the periphlebitis. Although we do not have histopathologic evidence that cytomegalovirus was the cause of these cases of periphlebitis, we believe that periphlebitis may be a previously unrecognized finding of cytomegalovirus retinitis in patients with acquired immunodeficiency syndrome. So far, there is no evidence implicating cytomegalovirus as the cause of acute frosted retinal periphlebitis in healthy patients.

Bioorganotin chemistry: a commentary on the reactions of organotin compounds with a cytochrome P-450 dependent monooxygenase enzyme system.

The biological oxidation of several tributyltin derivatives, by a cytochrome P-450 dependent monooxygenase enzyme system with reduced nicotinamideadeninedinucleotidephosphate as the essential cofactor, produced carbon-hydroxylated compounds identified as alpha-, beta-, gamma- and delta-hydroxybutyldibutyltin derivatives. The hydroxylation pattern and the lack of oxidative cleavage of tin-carbon bonds strongly suggest a free radical rather than an oxenoid mechanism, while the predominance of beta-carbon-hydroxylation further implies some role of the tin-carbon sigma electrons in directing the site of hydroxylation.

Pheromone biosynthetic pathways: Conversion of ipsdienone to (-)-ipsdienol, a mechanism for enantioselective reduction in the male bark beetle,Ips paraconfusus.

The enantiomeric composition of the pheromone components (+)-ipsdienoI, e.e. 87.6%, and (-)-ipsenol, e.e. 93.8%, produced by the male bark beetleIps paraconfusus (Scolytidae) under natural conditions was determined by HPLC separation of their diastereomeric ester derivatives. Males confined in an atmosphere of ipsdienone produced (-)-ipsdienol, e.e. 28%, and (-)-ipsenol, e.e. 86%, indicating an enantiomeric selectivity in the conversion of the ketone to the alcohols. These findings demonstrate an enantioselective conversion mechanism in the biosynthetic pathway to the pheromones from myrcene, a host-plant terpene.