Low-intensity focused ultrasound to the posterior insula reduces temporal summation of pain.

BACKGROUND: The insula and dorsal anterior cingulate cortex (dACC) are core brain regions involved in pain processing and central sensitization, a shared mechanism across various chronic pain conditions. Methods to modulate these regions may serve to reduce central sensitization, though it is unclear which target may be most efficacious for different measures of central sensitization. OBJECTIVE/HYPOTHESIS: Investigate the effect of low-intensity focused ultrasound (LIFU) to the anterior insula (AI), posterior insula (PI), or dACC on conditioned pain modulation (CPM) and temporal summation of pain (TSP). METHODS: N = 16 volunteers underwent TSP and CPM pain tasks pre/post a 10 min LIFU intervention to either the AI, PI, dACC or Sham stimulation. Pain ratings were collected pre/post LIFU. RESULTS: Only LIFU to the PI significantly attenuated pain ratings during the TSP protocol. No effects were found for the CPM task for any of the LIFU targets. LIFU pressure modulated group means but did not affect overall group differences. CONCLUSIONS: LIFU to the PI reduced temporal summation of pain. This may, in part, be due to dosing (pressure) of LIFU. Inhibition of the PI with LIFU may be a future potential therapy in chronic pain populations demonstrating central sensitization. The minimal effective dose of LIFU for efficacious neuromodulation will help to translate LIFU for therapeutic options.

Noninvasive neuromodulation of subregions of the human insula differentially affect pain processing and heart-rate variability: a within-subjects pseudo-randomized trial.

ABSTRACT: The insula is an intriguing target for pain modulation. Unfortunately, it lies deep to the cortex making spatially specific noninvasive access difficult. Here, we leverage the high spatial resolution and deep penetration depth of low-intensity focused ultrasound (LIFU) to nonsurgically modulate the anterior insula (AI) or posterior insula (PI) in humans for effect on subjective pain ratings, electroencephalographic (EEG) contact heat-evoked potentials, as well as autonomic measures including heart-rate variability (HRV). In a within-subjects, repeated-measures, pseudo-randomized trial design, 23 healthy volunteers received brief noxious heat pain stimuli to the dorsum of their right hand during continuous heart-rate, electrodermal, electrocardiography and EEG recording. Low-intensity focused ultrasound was delivered to the AI (anterior short gyrus), PI (posterior longus gyrus), or under an inert Sham condition. The primary outcome measure was pain rating. Low-intensity focused ultrasound to both AI and PI similarly reduced pain ratings but had differential effects on EEG activity. Low-intensity focused ultrasound to PI affected earlier EEG amplitudes, whereas LIFU to AI affected later EEG amplitudes. Only LIFU to the AI affected HRV as indexed by an increase in SD of N-N intervals and mean HRV low-frequency power. Taken together, LIFU is an effective noninvasive method to individually target subregions of the insula in humans for site-specific effects on brain biomarkers of pain processing and autonomic reactivity that translates to reduced perceived pain to a transient heat stimulus.

Prognostic Factors and Nomogram for Choroid Plexus Tumors: A Population-Based Retrospective Surveillance, Epidemiology, and End Results Database Analysis.

Background: Choroid plexus tumors (CPTs) are rare neoplasms found in the central nervous system, comprising 1% of all brain tumors. These tumors include choroid plexus papilloma (CPP), atypical choroid plexus papilloma (aCPP), and choroid plexus carcinoma (CPC). Although gross total resection for choroid plexus papillomas (CPPs) is associated with long-term survival, there is a scarcity of prospective data concerning the role and sequence of neoadjuvant therapy in treating aCPP and CPC. Methods: From the years 2000 to 2019, 679 patients with CPT were identified from the Surveillance, Epidemiology, and End Result (SEER) database. Among these patients, 456 patients had CPP, 75 patients had aCPP, and 142 patients had CPC. Univariate and multivariable Cox proportional hazard models were run to identify variables that had a significant impact on the primary endpoint of overall survival (OS). A predictive nomogram was built for patients with CPC to predict 5-year and 10-year survival probability. Results: Histology was a significant predictor of OS, with 5-year OS rates of 90, 79, and 61% for CPP, aCPP, and CPC, respectively. Older age and African American race were prognostic for worse OS for patients with CPP. Older age was also associated with reduced OS for patients with aCPP. American Indian/Alaskan Native race was linked to poorer OS for patients with CPC. Overall, treatment with gross total resection or subtotal resection had no difference in OS in patients with CPP or aCPP. Meanwhile, in patients with CPC, gross total resection (GTR) was associated with significantly better OS than subtotal resection (STR) only. However, there is no difference in OS between patients that receive GTR and patients that receive STR with adjuvant therapy. The nomogram for CPC considers types of treatments received. It demonstrates acceptable accuracy in estimating survival probability at 5-year and 10-year intervals, with a C-index of 0.608 (95% CI of 0.446 to 0.77). Conclusions: This is the largest study on CPT to date and highlights the optimal treatment strategies for these rare tumors. Overall, there is no difference in OS with GTR vs. STR in CPP or aCPP. Furthermore, OS is equivalent for CPC with GTR and STR plus adjuvant therapy.

Low-Intensity Focused Ultrasound to the Human Dorsal Anterior Cingulate Attenuates Acute Pain Perception and Autonomic Responses.

The dorsal anterior cingulate cortex (dACC) is a critical brain area for pain and autonomic processing, making it a promising noninvasive therapeutic target. We leverage the high spatial resolution and deep focal lengths of low-intensity focused ultrasound (LIFU) to noninvasively modulate the dACC for effects on behavioral and cardiac autonomic responses using transient heat pain stimuli. A N = 16 healthy human volunteers (6 M/10 F) received transient contact heat pain during either LIFU to the dACC or Sham stimulation. Continuous electroencephalogram (EEG), electrocardiogram (ECG), and electrodermal response (EDR) were recorded. Outcome measures included pain ratings, heart rate variability, EDR response, blood pressure, and the amplitude of the contact heat-evoked potential (CHEP).LIFU reduced pain ratings by 1.09 ± 0.20 points relative to Sham. LIFU increased heart rate variability indexed by the standard deviation of normal sinus beats (SDNN), low-frequency (LF) power, and the low-frequency/high-frequency (LF/HF) ratio. There were no effects on the blood pressure or EDR. LIFU resulted in a 38.1% reduction in the P2 CHEP amplitude. Results demonstrate LIFU to the dACC reduces pain and alters autonomic responses to acute heat pain stimuli. This has implications for the causal understanding of human pain and autonomic processing in the dACC and potential future therapeutic options for pain relief and modulation of homeostatic signals.

Central Nervous System Lymphoproliferative Disorder Secondary to Methotrexate: A Systematic Literature Review and Case Illustration.

BACKGROUND: Methotrexate is an immunosuppressant commonly used to treat inflammatory conditions, such as rheumatoid arthritis. However, albeit exceedingly rare, it can have serious adverse effects within the central nervous system (CNS), such as methotrexate-associated lymphoproliferative disorder (MTX-LPD). Literature describing the natural history, treatment options, and clinical outcomes of patients with CNS MTX-LPD remains sparse. METHODS: We present a systematic literature review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and a case illustration of CNS MTX-LPD. RESULTS: A systematic review of the literature revealed 12 published cases of CNS MTX-LPD, plus the case presented herein, for a total of 13 included cases. The most common indication for MTX was rheumatoid arthritis. The most common treatment for the LPD was MTX cessation (12, 92.3%), adjunct chemotherapy (2, 15.4%), total tumor resection (3, 23.1%), or steroid therapy (1, 7.7%). Treatment usually led to improvement of neurological symptoms (9, 69.2%) along with regression of the lesions (3, 23.1%) with no recurrence (6, 46.2%). Death was reported in four cases (30.8%) with a mean time from onset of 11 months. CONCLUSIONS: CNS MTX-LPD should be considered in the differential diagnosis for patients who are taking MTX presenting with neurologic symptoms, as immediate withdrawal of MTX has demonstrated good prognosis.

Co-occurrence of dural arteriovenous fistula and meningioma: A rare case and systematic review.

Background: The coexistence of meningioma and dural arteriovenous fistula (dAVF) is a rare, but highly complex condition. Various pathophysiological mechanisms underlie intracranial meningiomas with continuous or distant dAVFs. We describe a case of coexisting meningioma and dAVF with a systematic review of the literature. Result: Including the present case, there are 21 reported cases of coexisting intracranial dAVF and meningioma. The patients' ages ranged from 23 to 76 years, with a mean age of 61 years. The most common presenting symptom was headache. The dAVFs were commonly located at the transverse-sigmoid sinus (43%) and superior sagittal sinus (24%). The most common meningioma locations were the tentorium and parietal convexity. In 76% of the cases, the meningioma occluded the sinus. The most common dAVF treatment was transcatheter arterial embolization, followed by tumor resection (52%). Among the 20 cases with available outcome data, 90% reported favorable outcomes. Conclusion: This report highlights some of the features of coexisting dAVF and meningioma and presents a systematic review of other reports on this phenomenon. Through an in-depth analysis of the literature, we highlight some of the leading theories regarding the causes of concomitant dAVF and meningiomas. Our report supports one of the leading theories that impaired venous return, whether through the occlusion of sinuses or sinus manipulation during surgery, plays a role in the development of dAVF. Further understanding may help guide future clinical decision-making and surgical planning.

Non-invasive neuromodulation of sub-regions of the human insula differentially affect pain processing and heart-rate variability.

The insula is a portion of the cerebral cortex folded deep within the lateral sulcus covered by the overlying opercula of the inferior frontal lobe and superior portion of the temporal lobe. The insula has been parsed into sub-regions based upon cytoarchitectonics and structural and functional connectivity with multiple lines of evidence supporting specific roles for each of these sub-regions in pain processing and interoception. In the past, causal interrogation of the insula was only possible in patients with surgically implanted electrodes. Here, we leverage the high spatial resolution combined with the deep penetration depth of low-intensity focused ultrasound (LIFU) to non-surgically modulate either the anterior insula (AI) or posterior insula (PI) in humans for effect on subjective pain ratings, electroencephalographic (EEG) contact head evoked potentials (CHEPs) and time-frequency power as well as autonomic measures including heart-rate variability (HRV) and electrodermal response (EDR). N = 23 healthy volunteers received brief noxious heat pain stimuli to the dorsum of their right hand during continuous heart-rate, EDR and EEG recording. LIFU was delivered to either the AI (anterior short gyrus), PI (posterior longus gyrus) or under an inert sham condition time-locked to the heat stimulus. Results demonstrate that single-element 500 kHz LIFU is capable of individually targeting specific gyri of the insula. LIFU to both AI and PI similarly reduced perceived pain ratings but had differential effects on EEG activity. LIFU to PI affected earlier EEG amplitudes around 300 milliseconds whereas LIFU to AI affected EEG amplitudes around 500 milliseconds. In addition, only LIFU to the AI affected HRV as indexed by an increase in standard deviation of N-N intervals (SDNN) and mean HRV low frequency power. There was no effect of LIFU to either AI or PI on EDR or blood pressure. Taken together, LIFU looks to be an effective method to individually target sub-regions of the insula in humans for site-specific effects on brain biomarkers of pain processing and autonomic reactivity that translates to reduced perceived pain to a transient heat stimulus. These data have implications for the treatment of chronic pain and several neuropsychological diseases like anxiety, depression and addiction that all demonstrate abnormal activity in the insula concomitant with dysregulated autonomic function.

Evaluation of a Novel Acoustic Coupling Medium for Human Low-Intensity Focused Ultrasound Neuromodulation Applications.

OBJECTIVE: Single-element low-intensity focused ultrasound (LIFU) is an emerging form of human neuromodulation. Current coupling methods are impractical for clinical bedside use. Here, we evaluate commercially available high-viscosity gel polymer matrices as couplants for human LIFU neuromodulation applications. METHODS: We first empirically tested the acoustic transmission of three densities at 500 kHz and then subjected the gel with the least acoustic attenuation to further tests of the effect of thickness, frequency, de-gassing and production variability. RESULTS: The highest-density gel had the lowest acoustic attenuation (3.3%) with low lateral (<0.5 mm) and axial (<2 mm) beam distortion. Different thicknesses of the gel up to 10 mm did not appreciably affect results. The gel polymers exhibited frequency-dependent attenuation at 1 and 3 MHz up to 86.6%, as well as significant beam distortion >4 mm. Poor de-gassing methods also increased pressure attenuation at 500 kHz up to 59.6%. Standardized methods of making these gels should be established to reduce variability. CONCLUSION: Commercially available de-gassed, high-density gel matrices are a low-cost, easily malleable, low-attenuation and distortion medium for the coupling of single-element LIFU transducers for human neuromodulation applications at 500 kHz.

Depressed skull fracture compressing eloquent cortex causing focal neurologic deficits.

BACKGROUND: Depressed skull fractures are typically the consequence of high-impact injuries with inward buckling of the cranium. The majority of depressed skull fractures are managed conservatively in the absence of dural violation, sinus involvement, significant underlying hematoma, depressed fragment greater than 1 cm, wound infection, or gross wound contamination. Even in the presence of any of the aforementioned criteria, cranioplasty is typically considered an urgent procedure rather than a neurosurgical emergency. Rarely, a depressed fracture fragment can cause focal neurologic deficit(s) due to direct compression of the underlying eloquent cortex. CASE DESCRIPTION: A 40-year-old male presented to the emergency department after a mechanical fall with a left central facial nerve palsy, left hemiplegia, left hemianesthesia, and fixed right gaze deviation. The neurologic deficits observed were attributed to a combination of blunt force trauma to the head (i.e., coup-contrecoup injury) and the depressed fracture fragment compressing the underlying eloquent cortex. He underwent emergent cranioplasty with fragment elevation within 2 hours of the traumatic injury. At 6-month follow-up, he regained full neurologic function without any residual deficits. CONCLUSIONS: Our experience highlights a rare indication for emergent cranioplasty with an excellent functional outcome attributable to immediate fracture elevation and decompression of eloquent cortex.

Synthesis, chirality-dependent conformational and biological properties of siRNAs containing 5'-(R)- and 5'-(S)-C-methyl-guanosine.

Various chemical modifications have been identified that enhance potency of small interfering RNAs (siRNAs) and that reduce off-target effects, immune stimulation, and toxicities of metabolites of these therapeutic agents. We previously described 5'-C-methyl pyrimidine nucleotides also modified at the 2' position of the sugar. Here, we describe the synthesis of 2'-position unmodified 5'-(R)- and 5'-(S)-C-methyl guanosine and evaluation of these nucleotides in the context of siRNA. The (R) isomer provided protection from 5' exonuclease and the (S) isomer provided protection from 3' exonuclease in the context of a terminally modified oligonucleotide. siRNA potency was maintained when these modifications were incorporated at the tested positions of sense and antisense strands. Moreover, the corresponding 5' triphosphates were not substrates for mitochondrial DNA polymerase. Models generated based on crystal structures of 5' and 3' exonuclease oligonucleotide complexes with 5'-(R)- and 5'-(S)-C-methyl substituents attached to the 5'- and 3'-terminal nucleotides, respectively, provided insight into the origins of the observed protections. Structural properties of 5'-(R)-C-methyl guanosine incorporated into an RNA octamer were analysed by X-ray crystallography, and the structure explains the loss in duplex thermal stability for the (R) isomer compared with the (S) isomer. Finally, the effect of 5'-C-methylation on endoribonuclease activity has been explained.

Generation and validation of structurally defined antibody-siRNA conjugates.

Gene silencing by RNA interference (RNAi) has emerged as a powerful treatment strategy across a potentially broad range of diseases. Tailoring siRNAs to silence genes vital for cancer cell growth and function could be an effective treatment, but there are several challenges which must be overcome to enable their use as a therapeutic modality, among which efficient and selective delivery to cancer cells remains paramount. Attempts to use antibodies for siRNA delivery have been reported but these strategies use either nonspecific conjugation resulting in mixtures, or site-specific methods that require multiple steps, introduction of mutations, or use of enzymes. Here, we report a method to generate antibody-siRNA (1:2) conjugates (ARCs) that are structurally defined and easy to assemble. This ARC platform is based on engineered dual variable domain (DVD) antibodies containing a natural uniquely reactive lysine residue for site-specific conjugation to ß-lactam linker-functionalized siRNA. The conjugation is efficient, does not compromise the affinity of the parental antibody, and utilizes chemically stabilized siRNA. For proof-of-concept, we generated DVD-ARCs targeting various cell surface antigens on multiple myeloma cells for the selective delivery of siRNA targeting ß-catenin (CTNNB1). A set of BCMA-targeting DVD-ARCs at concentrations as low as 10 nM revealed significant CTNNB1 mRNA and protein knockdown.

Chirality Dependent Potency Enhancement and Structural Impact of Glycol Nucleic Acid Modification on siRNA.

Here we report the investigation of glycol nucleic acid (GNA), an acyclic nucleic acid analogue, as a modification of siRNA duplexes. We evaluated the impact of (S)- or (R)-GNA nucleotide incorporation on RNA duplex structure by determining three individual crystal structures. These structures indicate that the (S)-nucleotide backbone adopts a conformation that has little impact on the overall duplex structure, while the (R)-nucleotide disrupts the phosphate backbone and hydrogen bonding of an adjacent base pair. In addition, the GNA-T nucleobase adopts a rotated conformation in which the 5-methyl group points into the minor groove, rather than the major groove as in a normal Watson-Crick base pair. This observation of reverse Watson-Crick base pairing is further supported by thermal melting analysis of GNA-C and GNA-G containing duplexes where it was demonstrated that a higher thermal stability was associated with isoguanine and isocytosine base pairing, respectively, over the canonical nucleobases. Furthermore, it was also shown that GNA nucleotide or dinucleotide incorporation increases resistance against snake venom phosphodiesterase. Consistent with the structural data, modification of an siRNA with (S)-GNA resulted in greater in vitro potencies over identical sequences containing (R)-GNA. A walk of (S)-GNA along the guide and passenger strands of a GalNAc conjugate duplex targeting mouse transthyretin (TTR) indicated that GNA is well tolerated in the seed region of both strands in vitro, resulting in an approximate 2-fold improvement in potency. Finally, these conjugate duplexes modified with GNA were capable of maintaining in vivo potency when subcutaneously injected into mice.

Structural Basis of Duplex Thermodynamic Stability and Enhanced Nuclease Resistance of 5'-C-Methyl Pyrimidine-Modified Oligonucleotides.

Although judicious use of chemical modifications has contributed to the success of nucleic acid therapeutics, poor systemic stability remains a major hurdle. The introduction of functional groups around the phosphate backbone can enhance the nuclease resistance of oligonucleotides (ONs). Here, we report the synthesis of enantiomerically pure (R)- and (S)-5'-C-methyl (C5'-Me) substituted nucleosides and their incorporation into ONs. These modifications generally resulted in a decrease in thermal stability of oligonucleotide (ON) duplexes in a manner dependent on the stereoconfiguration at C5' with greater destabilization characteristic of (R)-epimers. Enhanced stability against snake venom phosphodiesterase resulted from modification of the 3'-end of an ON with either (R)- or (S)-C5'-Me nucleotides. The (S)-isomers with different 2'-substituents provided greater resistance against 3'-exonucleases than the corresponding (R)-isomers. Crystal structure analyses of RNA octamers with (R)- or (S)-5'-C-methyl-2'-deoxy-2'-fluorouridine [(R)- or (S)-C5'-Me-2'-FU, respectively] revealed that the stereochemical orientation of the C5'-Me and the steric effects that emanate from the alkyl substitution are the dominant determinants of thermal stability and are likely molecular origins of resistance against nucleases. X-ray and NMR structural analyses showed that the (S)-C5'-Me epimers are spatially and structurally more similar to their natural 5' nonmethylated counterparts than the corresponding (R)-epimers.

An RNAi therapeutic targeting antithrombin to rebalance the coagulation system and promote hemostasis in hemophilia.

Hemophilia A and B are inherited bleeding disorders characterized by deficiencies in procoagulant factor VIII (FVIII) or factor IX (FIX), respectively. There remains a substantial unmet medical need in hemophilia, especially in patients with inhibitory antibodies against replacement factor therapy, for novel and improved therapeutic agents that can be used prophylactically to provide effective hemostasis. Guided by reports suggesting that co-inheritance of prothrombotic mutations may ameliorate the clinical phenotype in hemophilia, we developed an RNA interference (RNAi) therapeutic (ALN-AT3) targeting antithrombin (AT) as a means to promote hemostasis in hemophilia. When administered subcutaneously, ALN-AT3 showed potent, dose-dependent, and durable reduction of AT levels in wild-type mice, mice with hemophilia A, and nonhuman primates (NHPs). In NHPs, a 50% reduction in AT levels was achieved with weekly dosing at approximately 0.125 mg/kg, and a near-complete reduction in AT levels was achieved with weekly dosing at 1.5 mg/kg. Treatment with ALN-AT3 promoted hemostasis in mouse models of hemophilia and led to improved thrombin generation in an NHP model of hemophilia A with anti-factor VIII inhibitors. This investigational compound is currently in phase 1 clinical testing in subjects with hemophilia A or B.

siRNA conjugates carrying sequentially assembled trivalent N-acetylgalactosamine linked through nucleosides elicit robust gene silencing in vivo in hepatocytes.

Asialoglycoprotein receptor (ASGPR) mediated delivery of triantennary N-acetylgalactosamine (GalNAc) conjugated short interfering RNAs (siRNAs) to hepatocytes is a promising paradigm for RNAi therapeutics. Robust and durable gene silencing upon subcutaneous administration at therapeutically acceptable dose levels resulted in the advancement of GalNAc-conjugated oligonucleotide-based drugs into preclinical and clinical developments. To systematically evaluate the effect of display and positioning of the GalNAc moiety within the siRNA duplex on ASGPR binding and RNAi activity, nucleotides carrying monovalent GalNAc were designed. Evaluation of clustered and dispersed incorporation of GalNAc units to the sense (S) strand indicated that sugar proximity is critical for ASGPR recognition, and location of the clustered ligand impacts the intrinsic potency of the siRNA. An array of nucleosidic GalNAc monomers resembling a trivalent ligand at or near the 3' end of the S strand retained in vitro and in vivo siRNA activity, similar to the parent conjugate design. This work demonstrates the utility of simple, nucleotide-based, cost-effective siRNA-GalNAc conjugation strategies.

Multivalent N-acetylgalactosamine-conjugated siRNA localizes in hepatocytes and elicits robust RNAi-mediated gene silencing.

Conjugation of small interfering RNA (siRNA) to an asialoglycoprotein receptor ligand derived from N-acetylgalactosamine (GalNAc) facilitates targeted delivery of the siRNA to hepatocytes in vitro and in vivo. The ligands derived from GalNAc are compatible with solid-phase oligonucleotide synthesis and deprotection conditions, with synthesis yields comparable to those of standard oligonucleotides. Subcutaneous (SC) administration of siRNA-GalNAc conjugates resulted in robust RNAi-mediated gene silencing in liver. Refinement of the siRNA chemistry achieved a 5-fold improvement in efficacy over the parent design in vivo with a median effective dose (ED50) of 1 mg/kg following a single dose. This enabled the SC administration of siRNA-GalNAc conjugates at therapeutically relevant doses and, importantly, at dose volumes of ≤1 mL. Chronic weekly dosing resulted in sustained dose-dependent gene silencing for over 9 months with no adverse effects in rodents. The optimally chemically modified siRNA-GalNAc conjugates are hepatotropic and long-acting and have the potential to treat a wide range of diseases involving liver-expressed genes.

Study of structural and dynamic characteristics of copper(II) amino acid complexes in solutions by combined EPR and NMR relaxation methods.

Structural features and dynamical behaviour of the copper(ii) bis-complexes with glycine, d-alanine, d-valine, l-serine, l-aspartic acid, l-glutamic acid, l-lysine, l-proline, and sarcosine were studied by combined EPR and NMR relaxation methods. The cis and trans isomers were unambiguously assigned and characterized by EPR data. It was found that addition of a salt background has an influence on the cis-trans isomer equilibrium in favour of the formation of the cis isomer. By comparison of NMRD, DFT computations, and structural data it was shown that only one water molecule is coordinated in the axial position of these complexes. The increased exchange rates of this molecule found for Cu(l-Asp)2(2-), Cu(l-Glu)2(2-), Cu(l-LysH)2(2+), and Cu(l-Pro)2 were attributed to its pushing out by side chain groups of the ligands. By simulation of NMRD profiles an increase of lifetimes of the copper(ii) 2nd coordination sphere water molecules was revealed in the presence of additional carboxylic, alcoholic, or ammonium groups of the ligands, as well as the pyrrolidine ring of proline. The very short lifetimes of the 2nd coordination sphere water molecules (4-13 ps at 298 K) were explained in terms of the Frank-Wen structural model by the existence of cavities which draw in quickly enough water molecules from the 2nd coordination sphere.

Metal-catalyzed 1,2-shift of diverse migrating groups in allenyl systems as a new paradigm toward densely functionalized heterocycles.

A general, mild, and efficient 1,2-migration/cycloisomerization methodology toward multisubstituted 3-thio-, seleno-, halo-, aryl-, and alkyl-furans and pyrroles, as well as fused heterocycles, valuable building blocks for synthetic chemistry, has been developed. Moreover, regiodivergent conditions have been identified for C-4 bromo- and thio-substituted allenones and alkynones for the assembly of regioisomeric 2-hetero substituted furans selectively. It was demonstrated that, depending on reaction conditions, ambident substrates can be selectively transformed into furan products, as well as undergo selective 6-exo-dig or Nazarov cyclizations. Our mechanistic investigations have revealed that the transformation proceeds via allenylcarbonyl or allenylimine intermediates followed by 1,2-group migration to the allenyl sp carbon during cycloisomerization. It was found that 1,2-migration of chalcogens and halogens predominantly proceeds via formation of irenium intermediates. Analogous intermediate can also be proposed for 1,2-aryl shift. Furthermore, it was shown that the cycloisomerization cascade can be catalyzed by Brønsted acids, albeit less efficiently, and commonly observed reactivity of Lewis acid catalysts cannot be attributed to the eventual formation of proton. Undoubtedly, thermally induced or Lewis acid-catalyzed transformations proceed via intramolecular Michael addition or activation of the enone moiety pathways, whereas certain carbophilic metals trigger carbenoid/oxonium type pathway. However, a facile cycloisomerization in the presence of cationic complexes, as well as observed migratory aptitude in the cycloisomerization of unsymmetrically disubstituted aryl- and alkylallenes, strongly supports electrophilic nature for this transformation. Full mechanistic details, as well as the scope of this transformation, are discussed.