Biallelic variants in COQ7 cause distal hereditary motor neuropathy with upper motor neuron signs.

COQ7 encodes a hydroxylase responsible for the penultimate step of coenzyme Q10 (CoQ10) biosynthesis in mitochondria. CoQ10 is essential for multiple cellular functions, including mitochondrial oxidative phosphorylation, lipid metabolism, and reactive oxygen species homeostasis. Mutations in COQ7 have been previously associated with primary CoQ10 deficiency, a clinically heterogeneous multisystemic mitochondrial disorder. We identified COQ7 biallelic variants in nine families diagnosed with distal hereditary motor neuropathy with upper neuron involvement, expending the clinical phenotype associated with defects in this gene. A recurrent p.Met1? change was identified in five families from Brazil with evidence of a founder effect. Fibroblasts isolated from patients revealed a substantial depletion of COQ7 protein levels, indicating protein instability leading to loss of enzyme function. High-performance liquid chromatography assay showed that fibroblasts from patients had reduced levels of CoQ10, and abnormal accumulation of the biosynthetic precursor DMQ10. Accordingly, fibroblasts from patients displayed significantly decreased oxygen consumption rates in patients, suggesting mitochondrial respiration deficiency. Induced pluripotent stem cell-derived motor neurons from patient fibroblasts showed significantly increased levels of extracellular neurofilament light protein, indicating axonal degeneration. Our findings indicate a molecular pathway involving CoQ10 biosynthesis deficiency and mitochondrial dysfunction in patients with distal hereditary motor neuropathy. Further studies will be important to evaluate the potential benefits of CoQ10 supplementation in the clinical outcome of the disease.

Computed tomography angiography as a confirmatory test for the diagnosis of brain death.

OBJECTIVE For a diagnosis of brain death (BD), ancillary testing is performed if patient factors prohibit a complete clinical examination and apnea test. The American Academy of Neurology (AAN) guidelines identify cerebral angiography (CA), cerebral scintigraphy, electroencephalography, and transcranial Doppler ultrasonography as accepted ancillary tests. CA is widely considered the gold standard of these, as it provides the most reliable assessment of intracranial blood flow. CT angiography (CTA) is a noninvasive and widely available study that is also capable of identifying absent or severely diminished intracranial blood flow, but it is not included among the AAN's accepted ancillary tests because of insufficient evidence demonstrating its reliability. The objective of this study was to assess the statistical performance of CTA in diagnosing BD, using clinical criteria alone or clinical criteria plus CA as the gold-standard comparisons. METHODS The authors prospectively enrolled 22 adult patients undergoing workup for BD. All patients had cranial imaging and clinical examination results consistent with BD. In patients who met the AAN clinical criteria for BD, the authors performed CA and CTA so that both tests could be compared with the gold-standard clinical criteria. In cases that required ancillary testing, CA was performed as a confirmatory study, and CTA was then performed to compare against clinical criteria plus CA. Radiographic data were evaluated by an independent neuroradiologist. Test characteristics for CTA were calculated. RESULTS Four patients could not complete the standard BD workup and were excluded from analysis. Of the remaining 18 patients, 16 met AAN criteria for BD, 9 of whom required ancillary testing with CA. Of the 16 patients, 2 who also required CA ancillary testing were found to have persistent intracranial flow and were not declared brain dead at that time. These patients also underwent CTA; the results were concordant with the CA results. Six patients who were diagnosed with BD on the basis of clinical criteria alone also underwent CA, with 100% sensitivity. For all 18 patients included in the study, CTA had a sensitivity of 75%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 33%. CONCLUSIONS Clinical examination with or without CA remains the gold standard in BD testing. Studies assessing the statistical performance of CTA in BD testing should compare CTA to these gold standards. The statistical performance of CTA in BD testing is comparable to several of the nationally accepted ancillary tests. These data add to the growing medical literature supporting the use of CTA as a reliable ancillary test in BD testing.

Diabetic foot complications in a northern Canadian Aboriginal community.

BACKGROUND: Limited access to basic foot care and protective footwear may contribute to diabetic foot complications. The purpose of this study was to determine the prevalence of foot complications, ongoing foot care, and footwear use in diabetic subjects in a remote northern Canadian Aboriginal community. METHODS: This was a cross-sectional cohort study of 169 diabetic people, including interview, physical examination, and retrospective chart review. RESULTS: The mean age of the 169 diabetic individuals in the study was 56 +/- 12 years and their duration of diabetes 10 +/- 7 years. There were 139 (82%) individuals who had 418 diabetic foot complications (average, 3.0 complications per subject with complications), including toenail pathology, foot and ankle deformities, calluses, impaired pulses, neuropathy, past or present ulcer, amputation, and Charcot arthropathy. Risk classification showed that 69 (41%) individuals were at risk for future ulceration. Fifty-five (33%) individuals had inadequate footwear for their foot risk category, and only 11 (17%) of 66 individuals in the higher risk categories (categories 2 and 3) had suitable footwear. In a 7-year period, only 0.7 screening foot examinations per diabetic subject per year were documented. However, during this period, foot problems accounted for 498 (18%) local emergency room visits, 359 (16%) hospitalization days, 109 (11%) nonemergency transfers, and 4 (6%) emergency transfers to a tertiary care hospital. CONCLUSIONS: Foot and ankle complications of diabetes in this remote Aboriginal community were common and associated with substantial morbidity. Preventive diabetic foot screening examinations and footwear were inadequate. The results suggest that programs for prevention and early detection of complications are needed, including foot screening, provision of appropriate footwear, and foot care.

The differential mortality of Glasgow Coma Score in patients with and without head injury.

IMPORTANCE: The GCS was created forty years ago as a measure of impaired consciousness following head injury and thus the association of GCS with mortality in patients with traumatic brain injury (TBI) is expected. The association of GCS with mortality in patients without TBI (non-TBI) has been assumed to be similar. However, if this assumption is incorrect mortality prediction models incorporating GCS as a predictor will need to be revised. OBJECTIVE: To determine if the association of GCS with mortality is influenced by the presence of TBI. DESIGN/SETTING/PARTICIPANTS: Using the National Trauma Data Bank (2012; N=639,549) we categorized patients as isolated TBI (12.8%), isolated non-TBI (33%), both (4.8%), or neither (49.4%) based on the presence of AIS codes of severity 3 or greater. We compared the ability GCS to discriminate survivors from non-survivors in TBI and in non-TBI patients using logistic models. We also estimated the odds ratios of death for TBI and non-TBI patients at each value of GCS using linear combinations of coefficients. MAIN OUTCOME MEASURE: Death during hospital admission. RESULTS: As the sole predictor in a logistic model GCS discriminated survivors from non-survivors at an acceptable level (c-statistic=0.76), but discriminated better in the case of TBI patients (c-statistic=0.81) than non-TBI patients (c-statistic=0.70). In both unadjusted and covariate adjusted models TBI patients were about twice as likely to die as non-TBI patients with the same GCS for GCS values<8; for GCS values>8 TBI and non-TBI patients were at similar risk of dying. CONCLUSIONS: A depressed GCS predicts death better in TBI patients than non-TBI patients, likely because in non-TBI patients a depressed GCS may simply be the result of entirely reversible intoxication by alcohol or drugs; in TBI patients, by contrast, a depressed GCS is more ominous because it is likely due to a head injury with its attendant threat to survival. Accounting for this observation into trauma mortality datasets and models may improve the accuracy of outcome prediction.

Anterior cervical discectomy and fusion involving a polyetheretherketone spacer and bone morphogenetic protein.

OBJECT: The authors reviewed clinical and radiographic outcomes in patients who had undergone anterior cervical discectomy and fusion (ACDF) involving the placement of polyetheretherketone (PEEK) spacers filled with recombinant human bone morphogenetic protein (rhBMP)-2. METHODS: Data obtained in 24 cases were retrospectively evaluated. The follow-up period ranged from 12 to 16 months (mean 13 months). Fifteen patients presented with radiculopathy, eight with myeloradiculopathy, and one with quadriparesis. Single-level ACDF was performed in 12 patients, two-level ACDF in nine, and three-level ACDF in three. Clinical outcomes were assessed using Odom criteria, and fusion was assessed by examining flexion-extension radiographs and computerized tomography scans in cases in which arthrodesis was questionable. Follow-up data were available for 23 patients. One patient died of medical complications unrelated to surgery 4 weeks after ACDF. Clinical outcomes were rated as good/excellent in 22 patients (95%) and fair in one (5%). Solid radiographically documented fusion, with evidence of solid bridging bone and no instability on flexion-extension x-ray films, was present in all cases. Complications included transient recurrent laryngeal nerve injury in one case, transient C-5 paresis in one, cerebrospinal fluid leakage in one, and transient dysphagia in two. CONCLUSIONS: Analysis of the results indicated that ACDF involving an rhBMP-2-filled PEEK spacer leads to good clinical outcomes (by Odum criteria) and solid fusion (even in multilevel cases) while avoiding the complications associated with harvesting iliac crest bone grafts.

Race and rehabilitation following spinal cord injury: equality of access for American Indians/Alaska Natives compared to other racial groups.

BACKGROUND: Representing 2 % of the general population, American Indians/Alaska Natives (AIs/ANs) were associated with 0.5 % (63) of the estimated 12,500 new cases of spinal cord injury (SCI) reported to the National Spinal Cord Injury Statistic Center in 2013. To date, the trend in health care disparities among AIs/ANs in the SCI community has not been examined. We sought to compare the rate of discharge to rehabilitation facilities (DRF) following traumatic SCI among adult AIs/ANs to other racial/ethnic groups for patients 15 to 64 years old. METHODS: Utilizing data from the National Trauma Data Bank (NTDB), we performed a retrospective analysis of SCI cases occurring between January 1, 2008 and December 31, 2012. SCI injuries were identified by International Classification of Diseases 9th Revision-Clinical Modification (ICD-9) codes or Abbreviated Injury Scale (AIS) scores. Injury severity was determined using the Trauma Mortality Prediction Model (TMPM) which empirically estimates each patient's probability of death given their individual complement of injuries. A series of seven logistic regression models were used to predict DRF between racial groups. RESULTS: Among the 29,443 patients in our cohort, 52.4 % were discharged to rehabilitation facilities. AIs/ANs comprised 1.1 % of the population, with 63.8 % dismissed to rehabilitation. AIs/ANs were significantly younger, had a higher probability of death, had longer hospital length of stay (HLOS), and were proportionately more likely to be discharged to rehabilitation compared to non-AIs. Regression models demonstrated increased odds of DRF for AIs/ANs compared to Hispanic and Asian racial/ethnic groups. CONCLUSIONS: American Indians/Alaska Natives who sustain SCI access rehabilitative care at a rate equitable to or greater than other races when multiple factors are taken into account. Further research is needed to assess the effect of those patient, physician, and health care system determinants as they relate to a patient's ability to access post-trauma rehabilitative care. Recommendations include advancing the level of racial, insurance, and geographic data necessary to adequately explore disparities related to such ubiquitously life-altering conditions as SCI.

Multimodality management of vertebral artery injury sustained during cervical or craniocervical surgery.

BACKGROUND: Iatrogenic vertebral artery (VA) injury is a rare but potentially devastating complication associated with cervical and craniocervical surgery. OBJECTIVE: To retrospectively evaluate treatment modalities and outcomes associated with iatrogenic VA injury. METHODS: Our institutional surgical database was queried for patients who underwent cervical or craniocervical surgery from January 1997 to August 2012. RESULTS: During this time period, 8213 patients underwent cervical or craniocervical surgery, and 17 (0.2%) cases of VA injury were identified. Eight (47%) of these injuries occurred during C1-2 instrumentation procedures. Primary microsurgical repair of the VA was performed in 5 patients. Other cases were managed by either surgical or endovascular VA occlusion. Of the 17 patients, 15 underwent immediate angiography, 9 of whom were ultimately treated by the use of endovascular techniques. CONCLUSION: VA injury is an uncommon complication of cervical and/or skull base surgery. Standardized management recommendations may help reduce complications associated with these rare but potentially devastating injuries.

Expanding neurosurgical care in Northwest Tanzania: the early experience of an initiative to teach neurosurgery at Bugando Medical Centre.

OBJECTIVE: Tanzania suffers from a severe lack of health practitioners trained in neurosurgical procedures. To address this problem, we have implemented an initiative, modeled after the experience of other pioneers in international neurosurgery, to establish cost-effective and sustainable neurosurgical care by teaching fundamental neurosurgical skills to local surgeons. In this report we describe our early experience in Northwest Tanzania and discuss the potential for this training model to improve neurosurgical care to a region in need. METHODS: Between September 2009 and October 2010, three residents and two attendings from our institution spent a total of 15 weeks at Bugando Medical Centre in Mwanza, Tanzania. During this time, we focused on teaching neurosurgical techniques, intraoperative decision-making, and clinical management skills to two local surgeons. The emphasis of our presence was on teaching and providing sustainable neurosurgical care. RESULTS: During this period, we performed 41 neurosurgical procedures with one of two local surgeons. The most common procedures performed were ventriculoperitoneal shunts (22%), myelomeningocele repairs (22%), and cranial trauma cases (17%). Five (12%) cases required the placement of spinal instrumentation. Thirty-nine (95%) patients remained stable or improved at discharge. There were 2 (5%) perioperative deaths. CONCLUSION: Although numerous challenges remain, our experience demonstrates the potential of this teaching model in providing sustainable neurosurgical care in Northwest Tanzania.

Transcranial minimally invasive neurosurgery for tumors.

This article considers common minimally invasive craniotomy approaches and the role of neuroendoscopy in the removal of extra-axial and intra-axial brain tumors, excluding those of the ventricle. The use of a keyhole craniotomy combined with a carefully selected trajectory can help avoid the disadvantages associated with a standard craniotomy. However, the decision to use endoscopy must be individualized based on the patient and tumor. Endoscopy can also be used as a surgical adjunct to improve tumor resection and to help protect neurovascular structures. Complications associated with minimally invasive tumor neurosurgery have been similar to those associated with conventional neurosurgical approaches, and available outcomes are promising.

Endocrinopathy, vision, headache, and recurrence after transsphenoidal surgery for Rathke cleft cysts.

BACKGROUND: Rathke cleft cyst can enlarge and become symptomatic. OBJECTIVE: To review the clinical data and results of all patients treated by the senior author for a Rathke cleft cyst. METHODS: A prospectively maintained surgical database, supplemented with updates from telephone conversations, of all patients presenting to the Barrow Neurological Institute from 1992 to the present was reviewed. RESULTS: Seventy-three patients (17 males, 56 females; mean age, 40 years; range, 5-80 years) underwent 77 resections. The mean length of follow-up was 27 months (range, 0-129 months). Presenting symptoms included headache (75%), followed by endocrinopathy (49%), and visual symptoms (39%). Preoperative chiasmopathy resolved in 75% and improved in 21% of the patients. Patients' preoperative endocrinopathy resolved at various rates, depending on the specific axis (29%-100%). Endocrinopathies were more likely to resolve in females than males. New postoperative endocrinopathies also occurred (0-8%). Headache resolved (68%) or improved (21%) in most patients. No patient had worsened headaches. Eight patients had a recurrence, 4 of whom underwent reoperation. The presence of squamous metaplasia was the only predictor of recurrence. CONCLUSION: Surgical fenestration and/or resection of Rathke cleft cyst via the transsphenoidal approach are a rational choice for surgical management of these lesions when symptomatic. In most cases, visual symptoms and headache can be expected to improve. New persistent endocrine deficits can be expected in a small percentage of patients, but preexisting endocrinopathies resolve in many patients.

Formation of painful seroma and edema after the use of recombinant human bone morphogenetic protein-2 in posterolateral lumbar spine fusions.

BACKGROUND: The use of bone morphogenetic proteins for fusion augmentation in spine surgery has increased dramatically in recent years. Information is continually emerging regarding the effectiveness and safety profile of these compounds. OBJECTIVE: We have noted an increased incidence in sterile seroma formation and painful edema after the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) for posterolateral lumbar fusion. We present a retrospective review to determine the incidence of seroma formation and to discuss its clinical implications. METHODS: We retrospectively reviewed the operative reports of patients who underwent posterolateral lumbar fusion with the addition of rhBMP-2. We identified all patients who required surgical exploration of a postoperative sterile seroma. RESULTS: Of the 130 patients who underwent posterolateral lumbar fusion with rhBMP-2, 6 (4.6%) were returned to the operating room for exploration of a sterile seroma. The total amount of rhBMP-2 delivered to the posterolateral space per patient was 2.1 to 14.7 mg (mean, 8.4 mg per patient). The patients were returned to the operating room 5 to 13 days (mean, 7.7 days) after their initial surgery, and infection was ruled out in all cases by intraoperative cultures. CONCLUSION: There seems to be an increased incidence of formation of sterile seroma and painful edema in the lumbar region after posterolateral fusion with rhBMP-2. This report, along with other series highlighting the potential complications of bone morphogenetic proteins, suggests that more caution should be used when these compounds are used. Further studies are required to better define the risks and benefits of using bone morphogenetic proteins for spine surgery.

Cavernous malformations of the brainstem presenting in childhood: surgical experience in 40 patients.

BACKGROUND: Brainstem cavernous malformations (BSCMs) are believed to compose 9% to 35% of all cerebral cavernous malformations, but these lesions have been reported in children in very limited numbers. OBJECTIVE: To review surgical outcomes of pediatric patients with BSCMs treated at 1 institution. METHODS: We retrospectively analyzed the course of 40 pediatric patients (19 males, 21 females; age range, 10 months to 18.9 years; mean, 12.3 years) who underwent surgery between 1984 and 2009. Age, sex, presenting symptoms, location of lesion, surgical approach, new postoperative deficits, Glasgow Outcome Scale score, recurrences, and resolution of baseline symptoms were recorded. RESULTS: Thirty-nine patients experienced hemorrhage before surgery. Lesion locations included the pons (n=22), midbrain (n=4), midbrain and thalamus (n=4), pontomesencephalic junction (n=3), medulla (n=3), pontomedullary junction (n=3), and cervicomedullary junction (n=1). Mean lesion size was 2.3 cm. Mean length of hospital stay was 10.7 days. The average clinical follow-up was 31.9 months in 36 patients with follow-up after discharge. At last follow-up, 5 patients had experienced symptoms and/or imaging consistent with rehemorrhage, either from a residual that enlarged or true recurrence (5.25% annual rebleed risk per patient after surgery); 2 required reoperation for further resection of cavernoma. Mean Glasgow Outcome Scale score was 4.2 on admission, 4.05 at discharge, and 4.5 at latest follow-up. Preoperative symptoms and deficits improved in 16 patients (40%). New neurological deficits developed in 19 patients (48%) and resolved in 9, leaving 10 patients (25%) with new permanent deficit. CONCLUSION: Compared with adults, pediatric patients with BCSMs tend to have larger lesions and higher rates of recurrence (regrowth of residual lesion). Given the greater life expectancy of children, surgical treatment seems warranted in those with surgically accessible lesions that have bled. Outcomes were similar to those in our adult series of patients with BSCMs.

Occipitoatlantal dislocation.

Occipitoatlantal dislocation (OAD) can be devastating. This injury may be fatal in many cases, but more survivors are reported because of improvements in diagnosis and treatment. This article describes the diagnosis and treatment of OAD. To diagnose and treat OAD appropriately, neurosurgeons must have a detailed understanding of the anatomy of the craniocervical junction. Various radiographic criteria are used to establish the diagnosis of OAD. A destabilizing injury such as OAD requires surgical fixation. Many surgical techniques are available for fixation of the craniocervical junction. Future studies will continue to refine the diagnostic criteria for OAD and to develop improved methods for craniocervical stabilization.

Surgical treatment of brainstem cavernous malformations.

BACKGROUND: The contemporary neurosurgeon is often confronted by cavernous malformations. Those located in the brainstem are particularly challenging METHODS: This article reviews published series on the natural history and surgical outcomes of these lesions and discusses the surgical approaches used at our institution for their resection. RESULTS: Despite their challenging location in the brainstem, appropriately selected lesions can be resected surgically with acceptable rates of morbidity and mortality. CONCLUSIONS: Our institutional philosophy on the surgical treatment of brainstem cavernous malformations reflects the substantial surgical experience of the senior author.

Cranial migration of a baclofen pump catheter associated with subarachnoid hemorrhage: case report.

OBJECTIVE: Cephalad migration of an indwelling intrathecal catheter within the spinal canal has rarely been described. Cranial subarachnoid hemorrhage (SAH) related to movement of this type of catheter has not been described. We report a case of SAH coincident with the migration of a free fragment of a baclofen pump catheter into the prepontine cistern. CLINICAL PRESENTATION: A baclofen pump system was removed from a 47-year-old man with spasticity related to multiple sclerosis. A section retained in the spinal canal extended up to the T9 level. Ten days after the pump and lower portion of the catheter were removed, the patient presented with a severe headache and a classic aneurysmal pattern of SAH. The patient's catheter was found to have migrated adjacent to the basilar artery at the level of the superior cerebellar artery. An extensive evaluation, including computed tomography angiography, digital subtraction angiography performed twice, magnetic resonance imaging, and magnetic resonance angiography, showed no apparent cause for the hemorrhage. Initially, the catheter was left in place. However, 5 months after the SAH, the patient elected to have the catheter removed. INTERVENTION: The catheter was pulled out from below through a C6-C7 laminoplasty without complications. The patient made an excellent recovery. DISCUSSION: Cephalad catheter migration is a rare phenomenon. The mechanism of rostral migration remains unclear. The forces that propel a free fragment of catheter under these circumstances seem to be sufficient to cause a small vessel to rupture and bleed. Given the lack of an observed arterial injury, we postulate that venous bleeding caused this hemorrhage.

The utility of onyx for preoperative embolization of cranial and spinal tumors.

OBJECTIVE: To assess the utility, technical factors, and complications associated with the use of Onyx (Micro Therapeutics, Inc., Irvine, CA) for preoperative embolization of cranial and spinal tumors. METHODS: We reviewed a prospectively accumulated database for patients in whom Onyx was used for preoperative embolization of cranial and spinal tumors over a 19-month period. The patients' demographic characteristics, tumor type and location, embolic agents used, arteries catheterized, and associated complications were assessed. Specific attention was focused on technical factors associated with the use of Onyx that differed from the use of other commonly used embolic materials. RESULTS: Ten patients (four female and six male; age range, 11-60 yr) underwent preoperative embolization with Onyx before cranial or spinal tumor resection. Tumors included three juvenile nasal angiofibromas, two meningiomas, two hemangioblastomas, two metastases (renal cell and thyroid), and one giant cell tumor. Onyx embolization was performed in 43 vessels over 11 treatment sessions. There were no complications related to the embolization procedures. Deep penetration of the embolic agent into the tumor was documented through preoperative imaging or surgical pathological specimens. CONCLUSION: Preoperative embolization of cranial and spinal tumors can be performed safely. Specific technical advantages of Onyx included deep penetration of lesions producing extensive tumor infarction, the ability to embolize extensive portions of the tumors through fewer arterial catheterizations, and the safety of catheter withdrawal despite often substantial reflux along the embolic catheter.

Evaluation of patients with spontaneous subarachnoid hemorrhage and negative angiography.

OBJECTIVE: The evaluation of patients with subarachnoid hemorrhage (SAH) with negative initial catheter-based angiography is a diagnostic challenge. Better diagnostic strategies based on hemorrhage patterns are needed. METHODS: We retrospectively investigated the yield of focused history taking, magnetic resonance imaging of the brain and cervical spine, follow-up vascular imaging, laboratory investigations, and craniotomy for vessel exploration in 100 patients with SAH and negative initial catheter-based angiography. RESULTS: The most common distribution of hemorrhage was in a "classic" aneurysmal pattern filling the basal cisterns or posterior fossa (44 patients). A cause was determined in 13 patients (13%), the most common of which was aneurysm (7 patients). Repeat angiography was the most useful diagnostic modality, detecting seven lesions. The yield of the second angiogram was best in patients with a classic hemorrhage pattern (10%) and worse in patients with a negative computed tomographic scan and positive lumbar puncture (0%). The most common reason that a lesion was not detected on initial angiography was aneurysmal thrombosis (five patients). Magnetic resonance imaging of the brain and cervical spine detected one cervical ependymoma. Factors that may contribute to SAH, such as antiplatelet agent use and drug use, were found in 13 patients (13%). Adjunctive laboratory studies alerted practitioners to modifiable risk factors. CONCLUSION: These data suggest useful modifications to current diagnostic paradigms for patients with angiographically negative spontaneous SAH.

Biotransformation of substituted pyridines with dioxygenase-containing microorganisms.

A series of 2-, 3- and 4-substituted pyridines was metabolised using the mutant soil bacterium Pseudomonas putida UV4 which contains a toluene dioxygenase (TDO) enzyme. The regioselectivity of the biotransformation in each case was determined by the position of the substituent. 4-Alkylpyridines were hydroxylated exclusively on the ring to give the corresponding 4-substituted 3-hydroxypyridines, while 3-alkylpyridines were hydroxylated stereoselectively on C-1 of the alkyl group with no evidence of ring hydroxylation. 2-Alkylpyridines gave both ring and side-chain hydroxylation products. Choro- and bromo-substituted pyridines, and pyridine itself, while being poor substrates for P. putida UV4, were converted to some extent to the corresponding 3-hydroxypyridines. These unoptimised biotransformations are rare examples of the direct enzyme-catalysed oxidation of pyridine rings and provide a novel synthetic method for the preparation of substituted pyridinols. Evidence for the involvement of the same TDO enzyme in both ring and side-chain hydroxylation pathways was obtained using a recombinant strain of Escherichia coli (pKST11) containing a cloned gene for TDO. The observed stereoselectivity of the side-chain hydroxylation process in P. putida UV4 was complicated by the action of an alcohol dehydrogenase enzyme in the organism which slowly leads to epimerisation of the initial (R)-alcohol bioproducts by dehydrogenation to the corresponding ketones followed by stereoselective reduction to the (S)-alcohols.

Dioxygenase-catalysed oxidation of disubstituted benzene substrates: benzylic monohydroxylation versus aryl cis-dihydroxylation and the meta effect.

Biotransformations of a series of ortho-, meta- and para-substituted ethylbenzene and propylbenzene substrates have been carried out, using Pseudomonas putida UV4, a source of toluene dioxygenase (TDO). The ortho- and para-substituted alkylbenzene substrates yielded, exclusively, the corresponding enantiopure cis-dihydrodiols of the same absolute configuration. However, the meta isomers, generally, gave benzylic alcohol bioproducts, in addition to the cis-dihydrodiols (the meta effect). The benzylic alcohols were of identical (R) absolute configuration but enantiomeric excess values were variable. The similar (2R) absolute configurations of the cis-dihydrodiols are consistent with both the ethyl and propyl groups having dominant stereodirecting effects over the other substituents. The model used earlier, to predict the regio- and stereo-chemistry of cis-dihydrodiol bioproducts derived from substituted benzene substrates has been refined, to take account of non-symmetric substituents like ethyl or propyl groups. The formation of benzylic hydroxylation products, from meta-substituted benzene substrates, without further cis-dihydroxylation to yield triols provides a further example of the meta effect during toluene dioxygenase-catalysed oxidations.