Cuevaenes A and B, new polyene carboxylic acids from Streptomyces sp. HKI 0180.
In the course of a screening for newmetabolites from strains of actinomycetes we disclosed Streptomyces sp. HKI 0180 as the producer of cuevaenes A (1) and B (2). The strain was isolated from a soil sample from the cave of Altamira (Spain). In this paper we report the production, isolation, structure elucidation and biological properties of 1 and 2 (Fig. 1). An agar slant culture of the above strain was used to inoculate a 500 ml Erlenmeyer flask containing 100ml of a seed medium composed of (g/liter): dextrose 15, soya bean meal 15, NaCl 5, CaCO3 1, KH2PO4 0.4, distilled water, pH 6.9. The producing medium contained (g/liter): mannitol 20, soya bean meal 20, distilled water, pH6.5.
Novel linear polyene antibiotics: linearmycins
Two novel linear polyene antibiotics, termed linearmycin A 1 and B 2, have been isolated from the mycelial extracts of Streptomyces sp. no. 30 and characterized as compounds 1 and 2, respectively. These compounds have similar, long linear structures terminating with amino and carboxylic acid groups, and show antifungal and antibacterial activity. The incorporation experiments using 13C-labelled acetate and propionate suggest that 1 is biosynthesized from one γ-aminobutyric acid, 24 acetate and 4 propionate molecules, by a polyketide pathway.
Modelling of Mooney viscosity relaxation in natural rubber
Abstract Better assessment of natural rubber (NR) quality and processability, through the identification of new attributes, is still a major challenge. With this scope, 12 model samples of natural polyisoprene and two of synthetic polyisoprene were characterized in terms of Mooney torque relaxation, using the standardized ISO289 method (ML(1+4)100, explained later in the Section 1 ). The main purpose of this study was to identify a model that gave a better fit for the experimental decay of Mooney torque over time (ML(t)=f(t)) than the usual power law model used before (Y=at−b, [G.M. Bristow, A.G. Sears, The use of novel parameters in the assessment of natural rubber processability, NR Technol. 18 (1987); H.G. Burhin, W. Spreutels, J.M. Campbell, MV2000 Mooney viscometer: Mooney relaxation measurements on raw polymers and compounded rubber stocks, Kautsch. Gummi Kunstst. 43 (1990) 431]). The results showed that a generalized Maxwell model, and the Wu–Abbott empirical model ( Y = 1 − a Ln ( t ) − ( b t / ( c + t ) ) ) [T. Wu, J.A. Abbott, Firmness and force relaxation characteristics of tomatoes stored intact or as slices, Postharvest Biol. Technol. 24 (2002) 59–68], recently used for describing stress relaxation of tomato flesh, allowed a better description of the relaxation curve for the samples studied than the power law or stretched exponential traditionally used. Moreover, the total relaxation time (τm) given by the generalized Maxwell model showed good correlation with the total gel content of the samples studied.