Kinetic resolution of primary allylic amines via palladium-catalyzed asymmetric allylic alkylation of malononitriles.

A range of primary allylic amines were resolved with selectivity factors of up to 491 through [Pd(allyl)Cl]2/(S)-BINAP-catalyzed and mesitylsulfonyl hydrazide-accelerated asymmetric allylic alkylation of malononitriles involving enantioselective C-N bond cleavage under aerobic conditions. Moreover, the reaction proved useful for the asymmetric synthesis of α-branched allyl-substituted malononitriles with high enantiopurity.

Palladium/copper-catalyzed oxidative arylation of terminal alkenes with aroyl hydrazides.

An unprecedented oxidative arylation reaction of terminal alkenes with simple aroyl hydrazides has been developed under aerobic conditions for the stereoselective synthesis of 1,2-disubstituted alkenes. A range of aroyl hydrazides underwent palladium/copper-catalyzed oxidative Mizoroki-Heck reaction with terminal alkenes open to air in a 1:1 mixture of dimethyl sulfoxide and acetonitrile to give structurally diverse 1,2-disubstituted alkenes in moderate to excellent yields with excellent regio- and E-selectivity. The reaction tolerated a wide variety of functional groups, such as alkoxy, hydroxy, amino, fluoro, chloro, bromo, cyano, nitro, ester, amide, imide, phosphine oxide, and sulfone groups, and, moreover, molecular oxygen and dimethyl sulfoxide were demonstrated to serve as terminal oxidants. This study provides a useful method for the stereoselective synthesis of 1,2-disubstituted alkenes through direct transformation of the vinylic CH bonds in terminal alkenes.

Intracellular and current source density analysis of pretectal input to the optic tectum of the frog.

OBJECTIVE: Electrophysiological examination of the ipsilateral pretectotectal projection has proved that pretectal cells elicit strong suppressive responses to the ipsilateral tectum. However, the neural mechanisms underlying the contralateral pretectotectal prejection are still obscure. The present study aimed to examine the synaptic nature of pretectal nuclei and contralateral tectal cells, and to demonstrate the spatiotemporal pattern of neuronal activity in the 2 main brain structures. METHODS: Intracellular recording and current source density (CSD) analysis were used to test the complexity of neuronal mechanism of pretectotectal information transfer. RESULTS: The pretectal stimulation elicited only one type of response on the contralateral tectum, the inhibitory postsynaptic potential (IPSP). The majority of contra-induced IPSPs were assumed to be polysynaptically driven. In the CSD analysis, only one sink with short latency was observed in each profile. The ipsilateral projection produced a prominent monosynaptic sink in layer 8 of tectum. Recipient neurons were located in layers 6 and 7 of tectum. The result confirmed former findings from ipsilateral intracellular recordings. CONCLUSION: These results suggest the following neuronal circuit: afferents from the pretectal nuclei broadly inhibit both tectal neuron, and since no second sink occurs in tectal layers, the pretectotectal excitatory afferents probably do not extend over the whole tectum, but are within limited state. The results of intracellular recording and CSD analysis further provide evidence of how pretectal afferent activity flows within the tectal laminae.

Response properties and receptive field organization of collision-sensitive neurons in the optic tectum of bullfrog, Rana catesbeiana.

OBJECTIVE: Many studies have reported that animals will display collision avoidance behavior when the size of retinal image of an object reaches a threshold. The present study aimed to investigate the neural correlates underlying the frog collision avoidance behavior. METHODS: Different types of visual stimuli simulating the retinal image of an approaching or a recessing object were generated by a computer and presented to the right eye of frog. A multielectrode array was used to examine the activity of collision-sensitive neurons, and single electrode recordings were employed to quantify visual parameter(s) of the frog collision-sensitive neurons. RESULTS: The multielectrode array revealed that 40 neurons in the optic tectum showed selective responsiveness to objects approaching on a direct collision course. The response profiles of these collision-sensitive neurons were similar to those of lobula giant movement detector (LGMD) in the locust or to those of neurons in the pigeon. However, the receptive field (RF) size of the frog neurons [(18.5+/-3.8) degrees, n=33)] was smaller than those of collision-sensitive neurons of the locust and the pigeon. Multielectrode recordings also showed that the collision-sensitive neurons were activated only when the focus of expansion of a looming retinal image was located within the center of its RF. There was a linear relationship between the parameter l/v (l denotes half-size of the object, v denotes approaching velocity) and time-to-collision (time difference between the peak of the neuronal activity and the predictive collision) in 16 collision-sensitive neurons. Theoretical consideration showed that the peak firing rate always occurred at a fixed delay of (60.1 +/- 39.5) ms (n=16) after the object had reached a constant angular size of (14.8 +/- 3.4) degrees (n=16) on the retina. CONCLUSION: The results may help clarify the mechanisms underlying the collision avoidance behavior in bullfrog.

An intracellular study of pretectal influence on the optic tectum of the frog, Rana catesbeiana.

OBJECTIVE: A few investigations have been reported about pretectal suppressive influences on the optic tectum of frog, but characteristics of tectal activity to pretectal input are left unknown. We made intracellular recordings to demonstrate the unexpected complexity in synaptic mechanisms involved in the suppressive influences of pretecal stimulation on the tectal cells. METHODS: In the present study, we investigated the neuronal activity evoked by pretectal (Lpd/P) nuclei stimulation using intracellular recording technique. RESULTS: The pretectal stimulation mainly elicited two types of responses in the ipsilateral tectum: an excitatory postsynaptic potential (EPSP) followed by an inhibitory postsynaptic potential (IPSP) and a pure IPSP. The latter predominated in the tectal cells responding to pretectal stimulation. In a few cells, biphasic hyperpolarization appeared under stronger stimulus intensities. The spikes of tecto-pretectal projecting cells elicited by antidromical stimulation were recorded in the ipsilateral tectum, which revealed reciprocal connections between the tectum and particular pretectal nuclei. The synaptic natures underlying pretecto-tectal information transformation have also been demonstrated. EPSPs with short latencies were concluded to be monosynaptic. Most IPSPs were generated through polysynaptic paths, but monosynaptic IPSPs were also recorded in the tectum. Nearly 98% of impaled tectal cells (except for antidromically projecting cells) showed inhibitory responses to pretectal stimulation. CONCLUSION: The results provide strong evidence that pretectal cells broadly inhibit tectal neurons as that has suggested by behavioral and extracellular recording studies.