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.
Towards the total synthesis of Calyculin C: preparation of the C13–C25 spirocyclic core
Abstract A stereoselective synthesis of the C 13 –C 25 of Calyculin C is described. Key steps involve the coupling of a terminal acetylene with a thiol ester and subsequent spirocyclisation using a double intramolecular hetero-Michael addition.
Senacarcin A, a new antitumor antibiotic produced by Streptomyces endus subsp. aureus.
Sir: We have isolated a new antitumor antibiotic, senacarcin A, from fermentation liquors of a species of Streptomyces. In this communication we report the production, isolation and physical properties of senacarcin A. The producing organism was isolated from a soil collected in Sakai, Osaka, Japan. The strain has been characterized taxonomically and has been designated Streptomyces endus subsp. uureus (NRRL 12174). The seed medium contained 20 g dextrin, 10 g glucose, 10 g peptone (Kyokuto Co.), I g yeast extract (Daigo Eiyo Co.), 0.5 g MgSO4.7H20 and 1 g calcium carbonate per liter of deionized water (pH 7.2 prior to sterilization). It was inoculated with the stock culture and incubated on a rotary shaker for 48 hours at 28°C. The seed culture was inoculated into the production medium at a rate of 5 % (v/v). The production medium contained 40 g fructose, 1g yeast extract (Kyokuto Co.), 2.2 g Lglutamic acid monosodium salt, 0.8 g L-histidine HCl, 1 g K2HPO4, 5 g MgSO4.7H2O, 10 mg ZnSO4.7H2O, 10 mg CaCl2.2H2O, 10 mg FeSO4 7H2O, 0.06 mg CoCl2.6H2O and 5 g CaCO3 (pH 7.2 prior to sterilization). The antibiotic was detected by paper disc assays against B. subtilis on agar plate. The peak titers were usually reached after 3 days incubation at 28°C. The broth was adjusted to pH 6 with sulfuric acid and filtered. The filtrate was applied to a column of Diaion HP 20 (Mitsubishi Kasei Co.),