Sterol biosynthesis inhibitors. Secondary effects and enhanced in vivo efficacy.

Sterol biosynthesis inhibitors such as the imidazoles and 1,2,4-triazoles are generally regarded as inhibitors of sterol C-14 demethylation. Neither the MIC values nor the data for direct interaction with the cytochrome P-450 responsible for oxidative C-14 methyl removal, however, fully explain the observed in vivo efficacy. The first generation of azoles, which includes clotrimazole and miconazole, has been supplemented by a second generation, and azoles of the new generation are capable of additional effects on sterol biosynthesis. With the new azoles, for example, delta 5 sterols may accumulate, the accumulation being due to additional sites of inhibition in sterol biosynthesis or to direct membrane-azole interactions. Ketoconazole, itraconazole, and vibunazole are representative of the azoles of the second generation. Finally, a third generation of azoles has been discovered. Azoles of this generation, which include fluconazole, show almost negligible in vitro potency against saprophytically grown fungi but excellent in vivo efficacy. These compounds specifically affect parasitic forms of fungi, thus blocking invasion processes, and interfere directly with the plasma membrane, as shown in leakage experiments. Such secondary effects obviously enhance in vivo potency.

Antimycotic efficacy of bifonazole in vitro and in vivo.

The new imadozolyl derivative 1-(p, alpha-diphenyl-benzyl)imidazole (bifonazole, Bay h 4502, Mycospor) shows in vitro the broad spectrum of activity characteristic of azole antimycotics. The intensity of activity under conventional test conditions is equivalent to that of clotrimazole. Further, concentrations of less than or equal to 5 micrograms/ml bifonazole have a fungicidal effect on dermatophytes, and a MIC value of less than or equal to 0.25 micrograms/ml has a maximal effect on Torulopsis glabrata. In ng concentrations bifonazole is effective on proliferating dermatophytes and pseudomycelia of Candida albicans. The resistance situation regarding bifonazole is favourable--as is typical of azole antimycotics. In animal experiments, topical application of concentrations of between 0.05 and 1% bifonazole as a cream or solution are extremely effective on guinea-pig trichophytosis. This is attributed to the therapeutically achievable fungicidal effect on dermatophytes and the long period of time the substance is retained in the skin. The sum of the experimental properties of bifonazole make it possible to recommend the active drug to be applied, once every 24 h, as a 1% cream or solution and the duration of therapy for these indications being reduced to 2-3 weeks.

[Concepts for the synthesis of new biologically active substances]. / Synthesekonzeptionen zu neuen biologischen Wirkstoffen.

Three concepts for the synthesis of biologically active compounds are discussed and illustrated by examples. In addition to the accidental finding of biologically active compounds, synthesized purely for chemical reasons, analogy models can serve as guidelines for synthesis. In the latter, naturally occurring or synthetic biologically active molecules are modified to optimize or alter the biological properties. A third approach for the synthesis of active substances is oriented according to the side of action. Models from biochemistry and molecular biology serve as a basis for synthesis planning.

Studies on the nature of the primary reactions of photosystem II in photosynthesis. II. The modification of the functional integrity of the photochemical active centers of system II by a alpha-bromo-benzyl-malodinitril and accompyaning effects on chloroplasts.

The effect of alpha-bromo-alpha-benzylmalodinitril (BBMD) on the oxygen evolution and on the absorption changes at 515 nm and 704 nm has been investigated in spinach chloroplasts. It has been found: 1. Under repetitive flash excitation conditions, where the back reaction around system II is practically excluded for kinetical reasons, BBMD does not resotre the 515 nm absorption change in DCMU poisoned chloroplasts. 2. Under single flash excitation conditions, where the back reaction around system II becomes prominent in the presence of DCMU, BBMD moderately inhibits this back reaction. The deleterious effect is pronounced by preillumination with short flashes during the BBMD incubation period of the chloroplasts in the absence of DCMU. 3. Incubation of the chloroplasts with BBMD leads to an activity loss of oxygen evolution which increases with the time td between the repetitive short excitation flashes and with the dark incubation time. Preillumination during the incubation period with tbbmd significantly enhances the effect. 4. In the absence of artificial electron acceptors BBMD suppresses in DCMU poisoned chloroplasts the 704 nm absorption change reflecting an internal cyclic electron flow around system I. On the other hand the linear electron transport at system I mediated by DCIP plus ascorbate as electron donor couple and benzylviologen as electron acceptor is not distrubed by BBMD. 5. BBMD incubation of chloroplasts accelerates the decay rate of the field indicating 515 nm absorption change. Based on these experimental findings the conclusion has been drawn, that -- in contrast to the assumption of Brandon and Elgersma (Biochim. Biophys. Acta 292, 753--762 [1973]) -- BBMD does not accept electrons from the primary electron acceptor X 320 of system II in DCMU poisoned chloroplasts. BBMD rather acts as a system I electron acceptor. Furthermore, BBMD exerts deleterious effects on the center of photosystem II, accompanied by a weak ADRY-effect on the water-splitting enzyme system Y. As a tentative explanation of the BBMD-action on system II it is assumed that BBMD transforms the photochemical centers of system II into dissipative energy sinks.

[2-anilino-1,3,4-thiadiazoles, inhibitors of oxidative and photosynthetic phosphorylation (author's transl)]. / 2-Anilino-1.3.4-thiadiazole, Hemmstoffe der oxidativen und photosynthetischen Phsphorylierung

2-anilino-1,3,4-thiadiazoles carrying various substituents in the 5-position as well as in the benzene-ring were synthesized. The compounds were tested with rat-liver-mitochondria and with spinach-chloroplasts and revelaed to be potent uncouplers of both, oxidative and photosynthetic phosphorylation, with pI50-values rangeing from 6.79 to 4.05. At higher concentrations all compounds are inhibitors of the Hill-reaction. In mitochondria a fair correlation exists between pKa of the acidic NH-group and the uncoupling activity; a maximum is obtained around pKa equals 6.8, whereas in chloroplasts activity is shifted to more acid pKa-values. The compounds meet the requirements for uncouplers according to the chemi-osmotic theory, being lipophilic weak acids. N-methylation causes total loss of activity in mitochondrial oxidative phosphorylation. The ingibitory action on photosynthetic electron transport is located within photosystem II. This latter activity is almost independent of substituent effects in contrast to uncoupling of either respiratory- or photo-phosphorylation.