Activation of Ca2+-sensitive, large-conductance potassium (BK) channels in vascular smooth muscle cells (VSMCs) by local, ryanodine receptor-mediated Ca2+ signals (Ca2+ sparks) acts as a brake on pressure-induced (myogenic) vasoconstriction—a fundamental mechanism that regulates blood flow in small resistance arteries. Here, we report that physiological intraluminal pressure within resistance arteries activated cGMP-dependent protein kinase (PKG) in VSMCs through oxidant-induced formation of an intermolecular disulfide bond between cysteine residues. Oxidant-activated PKG was required to trigger Ca2+ sparks, BK channel activity, and vasodilation in response to pressure. VSMCs from arteries from mice expressing a form of PKG that could not be activated by oxidants showed reduced Ca2+ spark frequency, and arterial preparations from these mice had decreased pressure-induced activation of BK channels. Thus, the absence of oxidative activation of PKG disabled the BK channel-mediated negative feedback regulation of vasoconstriction. Our results support the concept of a negative feedback control mechanism that regulates arterial diameter through mechanosensitive production of oxidants to activate PKG and enhance Ca2+ sparks.

A practical and safe reduction methodology for the conversion of D 2 -isoxazolines to 1,3-aminols is developed using polymethylhydrosiloxane-Pd(OH) 2 /C. In presence of (Boc) 2 O, the isoxazoline was converted into N-Boc protected 1,3-aminol in a one-pot procedure.The importance of 1,3-aminols and b-amino acids is undisputed. 2 b-Amino acids have an enhanced proteolytic stability against their a-amino acid counterparts. 3 Similarly, the 1,3-aminohydroxy scaffold is present in hydroxylated amino acids, 4a sphingolipids 4b and amino sugars. 4c The 1,3-aminol functionality is generated in a straightforward manner by direct reduction of D 2 -isoxazolines and several reagents have been explored for this purpose. D 2 -Isoxazolines 5 in turn are prepared by [3+2] cycloaddition reactions between olefins and in situ generated nitrile oxides; the stereochemical outcome of which is well studied. Similarly, the reduction of isoxazolines to 1,3-aminols is achieved efficiently with Raney Ni-H 2 , 6 LiAlH 4 , 7 whereas reagents such as Me 4 NB(OAc) 3 H, NaCNBH 4 and Zn(BH 4 ) 2 are poor performers. 8 Studies, have revealed that this reduction proceeds in two ways to yield either 1,3-aminols 9 or ketoalcohols. 10 Several efficient procedures for the reduction of organic functional groups have reported using inert polymethylhydrosiloxane (PMHS) as a source of hydride after activation in the presence of various catalysts. 11 We recognized that PMHS would be an ideal reduction reagent of D 2 -isoxazoline 12 for 1,3-aminol synthesis (Scheme 1). Additionally, if (Boc) 2 O is added to the reaction medium, N-Boc protected products could be isolated. Scheme 1Initially, we investigated hydride addition to D 2 -isoxazoline ester 1a by treating with PMHS and di-t-butyl dicarbonate in the presence of Pd(OH) 2 /C in EtOH for 8 hours at 50°C. A conventional workup yielded the N-Boc protected aminol 1b in 85%, with the ester functionality being unaffected (entry 1) and without any formation of ketoalcohol. The diastereoselectivity of this reaction was found to be 67:33 as determined by NMR spectroscopic studies of the crude sample. 13 The major isomer is assigned as the syn-product based on literature precedence. 8aEncouraged by this finding, D 2 -isoxazoline 2a was subjected to hydrogenation under identical conditions to obtain the corresponding aminol 2b, again as a mixture of two diastereoisomers in 68:32 ratio. 14 Similar results were obtained in the reduction of four other D 2 -isoxazolines 3a, 4a, 5a, and 6a. In all the cases studied, over 80% yield of the product was isolated after simple workup and column chromatography. When 7a was subjected to similar conditions, afforded 7b in 82% yield, without affecting the bromo functionality (entry 7). D 2 -Isoxazolines (entry 8, 9, 10) resulting from cycloaddition of styrene and three different aldoximes also underwent smooth reduction to yield N-protected 1,3-aminols in good yield. It was found that this protocol holds equally well with respect to aliphatic as well as aromatic substrates (...

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