An expedient synthesis of spiroketals: model studies for the calyculin C16–C25 fragment
Abstract A new short strategy to prepare the spiroketal fragment of calyculins is presented. A novel Seyferth–Gilbert type homologation of hindered lactols to the corresponding alkynes has been achieved for the first time. The spirocyclization was achieved efficiently via a DIHMA (double intramolecular hetero-Michael addition) process of this hindered ynone. The spirocyclization rate is not dependent on the stereochemistry of the alkoxy substituent in the oxolane ring.
Endusamycin, a novel polycyclic ether antibiotic produced by a strain of Streptomyces endus subsp. aureus.
Endusamycin formerly called CP-63,517 (C47H77O14Na), is a novel polycyclic ether antibiotic produced by a new strain of Streptomyces endus subsp. aureus (ATCC 39574). Recovery, fractionation and purification were achieved using standard procedures. Forms include the endusamycin free acid, mp 95 approximately 105 degrees C, lambda max 232 nm (log E 4.16), [alpha]25D +47.4 degrees (c 0.5, methanol) and a crystalline sodium salt, mp 215 approximately 220 degrees C, lambda max 232 nm, (log E 4.15), [alpha]25D +25 degrees (c 0.5, methanol). The structure is shown below, Fig. 1. Endusamycin exhibited; antibacterial activity, in vitro against Gram-positive and anaerobic bacteria, effectiveness against coccidia in poultry, and stimulation of propionic acid production in an in vitro system.
Studies on the ionophorous antibiotics. XXIV. Leuseramycin, a new polyether antibiotic produced by Streptomyces hygroscopicus.
A new antibiotic leuseramycin has been isolated from the cultured mycelium of the strain of Streptomyces hygroscopicus TM-531. Physicochemical data, in particular those of 1H- and 13C-NMR spectra, revealed that leuseramycin is closely related to dianemycin in its structure, the former having a methyl group in place of the hydroxymethyl group at C-30. It is active against Gram-positive bacteria, some phytopathogenic fungi and some protozoa.