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In the first part of the lecture some new advances in the chemistry of sesquiterpenic lactones are discussed and the revised structures of some guaianolides and germacranolides are presented.

1. 1. The introduction of an electronegatively charged substituent group (phosphate, phosphite, sulfate) to the 5′-position of GpUpU codon increases markedly its template activity for [ 14 C]Val-tRNA binding to ribosomes. Dinucleoside phosphates GpU bearing the same substituents at the 5′-end also show a significant template activity. 2. 2. Bulky and hydrophobic electronegatively charged 5′-substituents (methyl phosphate, methanephosphonate) have a small effect upon the template activity of GpUpU codon. GpU derivatives containing these groups at the 5′-end are not active. The replacement of methyl phosphate group by a hydrophilic substituent (β-hydroxyethyl phosphate) increases the activity of GpUpU codon. 3. 3. Analogously, pGpCpU is a more efficient template for Ala-tRNA than GpCpU. The 5′-phosphate, phosphite, sulfate and methyl phosphate derivatives of GpC stimulate the binding of Ala-tRNA to ribosomes. 4. 4. The introduction of 3′-phosphate has no effect upon the stimulation activities in all cases studied.

Partially purified uridine kinases from 5-azacytidine-sensitive and -resistant leukemic cells of AKR mice were separated on a Sephadex G-200 column. The elution profile of both enzymes was similar although specific activity of uridine kinase from 5-azacytidine-resistant cells was more than 50% lower than that isolated from the parental cell line. The apparent Km constants with respect to the concentration of phosphate donor and acceptor were identical for both uridine kinases, while Vmax for enzymes from the resistant line were significantly decreased. The enzymes under study were tested for their sensitivity to SH-blocking agents—p-chloromercuribenzoate, N-ethylmaleimide and iodoacetamide—and to urea, trypsin and cytidine 5′-triphosphate. Inactivation following p-chloromercuribenzoate affected the activity of uridine kinase from sensitive cells more markedly than that of uridine kinase from resistant ones. When the feedback effect of cytidine 5′-triphosphate was examined, the results indicated, in both cases, a non-competitive inhibition with respect to phosphate acceptor, Ki constant being the same (0.079 mM). Furthermore, vi/vo ratios for the intact and trypsin-digested uridine kinases from both cell lines plotted against varying amounts of cytidine 5′-triphosphate yielded a single curve in each instance. The significance of these findings is discussed.

Aus Polypodium vulgare L. wurde ein Saponin, das Polypodosaponin (1), isoliert. Es geht bei der Isolierung mit Methanol leicht in das 26-O-Methyl-polypodosaponin (2) uber, an dem vorwiegend die Konstitution aufgeklart wurde. Dem zugehorigen Aglykon (26-O-Methyl-polypodogenin) konnte die Struktur eines 3β-Hydroxy-26ξ-methoxy-22ξ.26ξ-epoxy-6-oxo-5α-cholestens-(7) (4) zugeordnet werden. Im Saponin 2 ist die 3β-Hydroxygruppe an einen α-L-Rhamnopyranosyl-(1 -2)-β-D-glucopyranosyl-Rest gebunden. 2 besitzt typische Saponineigenschaften und stellt eine neue Variante der Steroidsaponine dar.