Cyclic voltammetry studies on substituted arenesulfonhydrazides

Additional Z and Boc groups on the vicinal nitrogen of sulfonyl hydrazines have no significant effect on the cathodic potential of the sulfonyl functions as measured by cyclic voltammetry, whereas a Boc group on the geminal nitrogen invariably gives rise to shifts of about 0.2 V to less negative potential similar to those previously observed for derivatives of amines.This work was supported by the Swedish Natural Science Research Council (NFR) and the Fundaçao para a Ciência e a Tecnologia (Portugal)

2-naphthalenesulfonyl as a tosyl substitute for protection of amino functions. Cyclic voltammetry studies on model sulfonamides and their preparative cleavage by reduction

With the aim to develop a practically useful, reductively more labile alternative to tosyl for protection of amino functions, initially a number of N-arenesulfonyl-protected heterocycles (pyrroles, imidazoles, indole, and carbazole) have been prepared and studied by cyclic voltammetry (CV). The recorded activation potentials vary from -1.32 to -1.99 V (vs SCE). In N-sulfonylazolides such as tosylindole the cathodic potentials are shifted by over 0.5 V compared to simple sulfonamides. An additional effect of the sulfonic acid component is also indicated. Among the compounds studied, 1- and 2-naphthalenesulfollylindole give CV peaks at about 0.4 and 0.2 V, respectively, less negative potential than tosylindole. To further investigate naphthalenesulfonyl for this purpose, we have also prepared a variety of simple 1- and 2-naphthalenesulfonyl derivatives and studied them similarly. They have activation potentials above -2.14 V and are all smoothly cleaved by Mg/MeOH. The latter reagent is capable of cleaving N-arenesulfonyl derivatives that give CV peaks above -2.30 V, whereas Al(Hg) requires potentials above about -1.7 V. Selective cleavage of 2-naphthalenesulfonyl in the presence of tosyl by Mg/MeOH is demonstrated. Several examples of reductive cleavage of arenesulfonyl derivatives with Mg/MeOH, Al(Hg), and electrolysis on a preparative scale are given.This work was supported by the Swedish Natural Science Research Council (NFR), the Swedish Research Council for Engineering Sciences (TFR), Carl Tryggers Stiftelse, Astra Draco AB, and the Fundacão para a Ciência e a Tecnologia (Portugal). B.N. gratefully acknowledges the RSC for a journals grant for international authors and the ISP for a fellowship, as well as the University of Yaoundé I for a leave of absence

Selective cathodic cleavage of unsymmetrical imidodicarbonates, acylcarbamates and diacylamides

A study of the selective cathodic cleavage of one of the alkoxycarbonyl or acyl groups from various imidodicarbonates, acylamides, and diacylamides is reported. The compounds investigated include all 15 possible combinations of the following groups in unsymmetrical N,N-diprotected derivatives of benzylamine: p-nitrobenzyloxycarbonyl, trichloroethyloxycarbonyl, toluene-p-sulfonyl, benzoyl, benzyloxycarbonyl, and tert-butyloxycarbonyl which can all be electrochemically cleavaged, except the last one. Initially the compounds were examined by cyclic voltammetry in order to measure the potentials associated with the cleavage of each group and afterwards they were electrolysed at constant potential in the presence of a proton donor. The following ranges in negative potential were recorded: 1.03-1.13 V [Z(NO2)], 1.8-2.14 V (Troc), 1.75-2.41 V (Tos), 1.88-2.52 V (Bz), and 2.83-2.9 V (Z), thus occasionally revealing a drastic effect of the auxiliary group. In the electrolytic experiments competitive attack by base occasionally led to mixtures of monoacylamides. However, all compounds apart from some of the trichloroethyloxycarbonyl derivatives could be selectively cleaved in 89-100% yields when an appropriate proton donor was used. Tentative explanations are given for the behaviour of the compounds studied and some conclusions are drawn

Long-term decline in northern pike (Esox lucius L.) populations in the Baltic Sea revealed by recreational angling data

In the Baltic Sea, the large predatory fish northern pike (Esox lucius L.) is important for both recreational fisheries and ecosystem functioning. As existing fishery-independent surveys do not adequately monitor pike populations, a general lack of knowledge on population status and trends poses challenges for management. Here we use recreational angling data as an alternative method to describe pike population development along the Swedish Baltic Sea coast from 1938 onwards and assess the change over time in potential mortality factors by estimating harvest by fisheries and consumption by large predators. Data from a Swedish national register on trophy-sized pike (>12 kg) showed that numbers and maximum sizes peaked in 1990-1995, after which declines in both metrics are evident. In logbooks from a sport fishing club in the Stockholm archipelago, a simultaneous decrease in maximum sizes of pike was observed, together with a decrease in the total number of pike caught per fishing day. Jointly, these data indicate a decline in the abundance of large pike since around 1990. While commercial pike fisheries in the Baltic Sea have decreased continuously since the 1950s, recreational fishing increased after 1985, when Swedish coastal waters were made open access to anglers. The declines in large pike starting in the 1990s could, thus, have been driven by an increase in mortality from recreational fisheries, which at the time primarily practiced catch and kill. Since the 2000s, bag and slot length limits, spawning closures, and a general increase in catch-and-release fishing has reduced the landings of pike in recreational fisheries. Despite these fisheries regulations and higher release rates the decline in catches of large pike has continued, indicating an effect of other mortality factors. The strong growth of grey seal (Halichoerus grypus) and great cormorant (Phalacrocorax carbo sinensis) populations suggest that predation pressure on pike has increased over time. In the Stockholm archipelago these two predators were estimated to remove 5-18 times (range based on different diet composition estimates) more pike biomass than total fisheries landings in 2014-2017. To improve the situation for northern pike in the Baltic Sea managers need to consider both fisheries restrictions and measures to decrease predation pressure and increase recruitment. Catch data from recreational fisheries may be used to evaluate such management efforts by providing information on the population development of this keystone species

Synthesis and cathodic cleavage of a set of substituted benzenesulfonamides including the corresponding tert-butyl sulfonylcarbamates: pKa of sulfonamides

From a series of Substituted benzenesulfonic acids, most of which have previously been employed for the protection of amino functions and including a few such known to facilitate cleavage by acid, benzylamides 1a-k have been derived and studied. Initially their electrochemical cleavage potentials were determined by cyclic voltammetry in order to further explore selective deprotection within this substance group. In parallel, the corresponding tert-butyl sulfonylcarbamates 2a-k have also been prepared and studied. Among the sulfonamides investigated S-N bond cleavage was found to take place over a wide range of potentials from -1.67 to -2.64 V (excluding the nitro derivative), the most acid-labile groups requiring more negative potentials, whereas this cleavage was facilitated by 0.19-0.30 V for the sulfonylcarbamates. Small scale electrolyses of 2 at controlled potential with determination of the cleavage products formed were subsequently performed. For the N-benzylbenzenesulfonamides 1, the pK(a)s in DMSO and in some cases also in water have been determined and found to be in the range 14.0-16.4 and 10.07-11.53, respectively

Enhancing reductive cleavage of aromatic carboxamides

[GRAPHICS] A set of aromatic and especially heteroaromatic N-benzyl carboxamides, derived from naphthalene, pyridine, pyrazine, and quinoline, and the corresponding tert-butyl acylcarbamates have been synthesized and studied by cyclic voltammetry with respect to facilitated reduction. The latter undergo regiospecific cleavage of their C(O)-N bonds under very mild reductive conditions with formation of Boc-protected (benzyl)amine in most cases in nearly quantitative yields, Examples of preparative cleavage by controlled potential electrolysis, activated aluminum, and NaBH4 are given

Dual protection of amino functions involving Boc

Protecting groups play a pivotal role in the synthesis of multifunctional targets and as amino functions often occur in this context, issues related to their protection become prominent. Primary amines are unique because they can accommodate two such groups. This review highlights various aspects related to the synthesis, properties and applications of products containing one or two Boc-groups resulting from dual protection of amines and amides. Attention is directed towards cases of facilitated cleavage due to mutual interaction between two protecting groups on the same nitrogen

Profesors Igors Danilāns: biobibliogrāfiskais rādītājs

Biobibliogrāfiskajā rādītājā ietverti profesora Igora Danilāna publicētie darbi no 1955.gada līdz 1999.gada jūnijam, kā arī literatūra par viņu