No abstract

“The following remarks consist partially of matter of fact, and partially of opinion. The former will be permanent; the latter must vary with the detection of error, or the improvement of knowledge. I hazard them with diffidence, and hope they will be examined with candour.” These declarations, which stem from the famous book “An Account of the Foxglove and some of its Medical Uses” by physician William Withering in 1785 in which he introduced preparations from digitalis leaves in the therapy of dropsy (cardiac failure), are cited here by the senior author because of his awareness of the difficulties in presenting a balanced report on his life‐long research project on the further development of digitalis. His decision to devote himself to digitalis research originated at the bedside, when as a physician he experienced the grim final stages of cardiac failure in which no real help for the patients is possible. Unfortunately, his research project did not fit into the research program decreed by the Ministry of Science of the German Democratic Republic, so that he was ordered to stop the digitalis project in favor of biomembrane studies. Fortunately, he got round the ban simply by labeling the digitalis‐like acting steroids as probes for the cell membrane‐located Na+/K+‐transporting ATPase which he had just recognized as the digitalis target (receptor) enzyme. These and other ventures by the authors are collated here for the first time. The aim of this review is to foster straightforward research for solving a major challenge: the development of steroidal drugs for the prevention and cure of cardiac failure.

Since 1985, several research groups have shown that a number of amino acids in the catalytic a-subunit of Na+/K +-ATPase more or less strongly modulate the affinity of a digitalis compound like ouabain to the enzyme. However, scrutiny of these findings by means of chimeric Na+/K+-ATPase constructs and monoclonal antibodies has recently revealed that the modulatory effect of most of these amino acids does not at all result from direct interaction with ouabain, but rather originates from longrange effects on the properties of the digitalis binding matrix. Starting from this knowledge, the present review brings together the various pieces of evidence pointing to the conclusion that the interface between two interacting a-subunits in the Na+/K+-ATPase protodimer (c~/3)2 provides the cleft for inhibitory digitalis intercalation.Key words: Na+/K+-transporting ATPase; Digitalis receptor; Binding cleft; Location; Property Na*/K+-ATPase is a complex of two catalytic ~-subunits and two catalytically inert fl-subunits, and a number of lipid molecules incorporated into the lipid bilayer of the plasma membrane. The cc-subunit contains about 1,012 amino acids. From the primary sequence, hydropathy analysis has been used to compute the local hydrophobicity and predict single-spanning s-helical segments that are long enough to traverse a 40 membrane (approximately 20 amino acids). The most recent 'working' model of the membrane topology of the enzyme, presented by Askew and Lingrel [14], comprises ten transmembrane segments (H1-H10) linked by five extracellularly disposed loops. Since the membrane topology models are constantly being revised to accommodate new findings, none of the defensible models (cf. Sweadner and Arystarkhova [15]) will be explicitly invoked here. Outcome of various attempts to identify the amino acids involved in the digitalis receptor site

trans-Pinocarveol findet sich frei und als Essigsaureester im atherischen 0 1 von Eucalyptus globulus 1). Wir untersuchten, ob bei der Einwirkung von Halogenwasserstoff eine analoge Umlagerung in das Camphansystem eintritt wie bei Pinenen zu Bornylhalogeniden. Durch Einleiten von HCI und HBr in Pinocarveol mit oder ohne Losungsmittel sowie bei niedrigen oder hoheren Temperaturen wurden stets die gleichen, sehr bestandigen und leicht sublimierenden Pinocarveol-hydrohalogenide I und I1 erhalten, die zum analytischen Nachweis dieses Terpenalkohols dienen konnen 2). Aus Pinocarveolestern entstanden flussige ~ster-h~drohalogenide (111 und IV), von denen I11 sich zum Pinocarveol-hydrochlorid (I) verseifen liel3. Pinocarvylmethyluther, aus dem Alkohol durch Uberfuhrung in das Alkoholat mit Natriumamid und Umsetzung mit Dimethylsulfat dargestellt, lagerte HBr zu Pinncarvylmethyluther-h~dro-brornid (V) ohne Umlagerung (IR-Spektren) an.Zinkstaub in siedendem ffthanol dehalogenierte das Hydrobromid 11 zu einem Geniisch stereoisomerer Pinocampheole (VI) vom Schmp. 59 -61 So (IR-Spektrum),wobei Umlagerung von der trans-in die cis-Reihe stattgefunden haben durfte.Chromsaureoxydation der Pinocarveol-hydrohalogenide I und I1 fiihrte zu den Pinorawon-hydrohalogeniden VII und VIII, in denen das Halogen noch fester gebunden ist als in I und 11, so daB alkoholische Alkalien ohne Einwirkung waren und VII sowie VIII durch kochende alkoholische Hydroxylamin-Losung in ihre Oxime iibergefuhrt werden konnten. *) R. MECGES, Diplomarbeit Univ. Leipzig 1959.

New aldimines were synthesized from the cardenolide strophantidin and cardenolide-glycosides erysimin and cymarin and included morpholine, nitrile, pyridine, furan, hydroxy-and methoxyphenyl, piperidine, and other derivatives. An effective modified method for synthesizing aldimines was proposed. 52 new compounds were synthesized. Their structures were confirmed by IR and PMR spectra and elemental analysis.We previously reported [1, 2] the synthesis of eight aldimines of strophantidin, some of which were slightly toxic cardiotonics, for example, adamantyliminostrophantidin [2].Therefore, it seemed advisable to continue research on the preparation of a broader set of new compounds with subsequent pharmacological screening. For this, we used amines of various structures.The starting natural compounds were the cardenolide strophantidin and the cardenolide-glycosides erysimin and cymarin, which have angular aldehydes [3]. These were synthesized by two methods. Organic compounds containing a free primary amine were reacted directly with the natural aldehydes by boiling in appropriate solvents and removing the water formed during the reaction by azeotropic distillation. It was found that the imines formed most rapidly and completely at the highest possible concentrations of the reactants, when the reaction mixture was like a melt. From the time such a state was reached, the reaction was finished usually within an hour.The second method was necessitated by the fact that primary amines are commonly sold as salts, more often as hydrochlorides. In these instances, the reaction was carried out in boiling solutions with sodium acetate.For both methods the course of the reactions was monitored by TLC or paper chromatography. The yields of the desired products were 60-80% of those calculated. The structures of products 1-52 were confirmed by elemental analysis and IR and PMR spectra. The IR spectra typically lacked absorption bands for aldehyde and contained absorption bands for C=N groups (1650 cm -1 ).During the synthesis of the cardenolide aldoximes we observed the rare case where two types of isomers, conformational (conformers) and geometrical (cis-trans or syn-anti), were formed simultaneously. The conformational isomers formed because free rotation around the C10-C19 single bond is restricted for steric reasons. We have previously reported this during the synthesis of cardenolide oximes [4] and demonstrated that the most stable of the two possible conformers is that in which the H atom of C19-H is oriented toward the angular methyl of the 18-CH 3 . This is completely consistent with the cardenolide aldimines and is confirmed by the following data. Strophantidin aldimines form complexes (green colored) with Cu ions that are soluble in organic solvents. The unshared pair of the N atom and the C3 and C5 OH groups (5) are involved in the complexation. The PMR spectra of the aldimines have signals for the angular 18-CH 3 methyl near 0.66-0.74 ppm, i.e., shifted to strong field. This is due to steric shielding of this group ...