Synthesis and in vitro evaluation of new wortmannin esters: potent inhibitors of phosphatidylinositol 3-kinase.

New C-11 esters of the fermentation product wortmannin have been synthesized, with some of them further derivatized at C-17. The new esters show greater inhibition of isolated phosphatidylinositol 3-kinase and increased cell cytotoxicity in a rapidly proliferating leukemia cell line, when compared to wortmannin. Reduction of the C-17 ketone caused a slight increase in activity, while acylation of this new alcohol caused severe loss of activity. With their increased activity, the new C-11 esters may be good candidates to explore the in vivo antitumor effects of phosphatidylinositol 3-kinase inhibitors.

Conversion of spinosyn A and spinosyn D to their respective 9- and 17-pseudoaglycones and their aglycones.

Forosamine at the 17-position of spinosyns A and D was hydrolyzed under mild acidic conditions to give the corresponding 17-pseudoaglycones. The tri-O-methylrhamnose at the 9-position of the 17-pseudoaglycone of spinosyn A was hydrolyzed under more vigorous acidic conditions to give the aglycone of spinosyn A. However, these conditions led to decomposition of the 17-pseudoaglycone of spinosyn D, presumably due to more facile protonation of the 5,6-double bond to produce a tertiary carbonium ion which undergoes further rearrangements. Spinosyns J and L (3'-O-demethyl spinosyn A and D, respectively) obtained from fermentation of biosynthetically-blocked mutant strains of Saccharopolyspora spinosa, were oxidized to give the corresponding 3'-keto-derivatives and the resultant keto-sugars were then beta-eliminated under basic conditions to give the 9-pseudoaglycones of spinosyns A and D respectively. Forosamine at the 17-position of the 9-pseudoaglycone of spinosyn D was then readily hydrolyzed to yield the aglycone of spinosyn D.

Synthesis, antimicrobial activity and in vivo fluorine NMR of a hexafluorinated derivative of tilmicosin.

A new fluorinated analog of tilmicosin was synthesized by the reductive amination of desmycosin with 3,5-bis(trifluoromethyl)piperidine. Despite an apparently small change in structure, the fluorinated analog had much less in vitro antimicrobial activity than tilmicosin and it failed to protect 3-day old chicks against a Pasteurella multocida challenge at 64 mg/kg sc. In a preliminary in vivo fluorine NMR experiment in a female Sprague-Dawley rat, a 19F NMR signal was detected in the liver one hour after ip administration of the fluorinated compound. Therefore, although this fluorinated derivative had less antimicrobial activity than tilmicosin, it may nevertheless provide a suitable model of tilmicosin for pharmacokinetic studies using in vivo fluorine NMR.

Synthesis and insecticidal activity of spinosyn analogs functionally altered at the 2'-,3'- and 4'-positions of the rhamnose moiety.

In an effort to increase the insecticidal activity of the spinosyn family of naturally occurring macrolides, the 2'-, 3'- and 4'-O-desmethyl-O-acetyl analogs and the 2'-, 3'-, and 4'-O-desmethoxy analogs have been synthesized. These analogs were prepared synthetically from the minor spinosyn factors H, J, K, L and Q either via direct acylation of the corresponding factor or deoxygenation of an intermediate xanthate. The acylated analogs were all more potent insecticides against Heliothis virescens larvae than their respective parent factors, but not as potent as spinosyns A or D. The deoxy analogs were also more potent insecticides than their respective parent factors. The 2'-desmethoxy analogs showed, for the first time, analogs with insecticidal potency against H. virescens greater than that of spinosyns A and D, indicating that polarity is not well tolerated in the rhamnose moiety of spinosyn A.

Structure of the new spiroketal-macrolide A82548A.

A new member of the spiroketal-containing macrolide class of fermentation-derived natural products was isolated from mycelial extracts of Streptomyces diastatochromogenes. The principal component, A82548A, was shown to possess a 22-membered macrolide ring system onto which was incorporated both a spiroketal and a hemiketal moiety. Relative stereochemistry was established by single crystal X-ray diffraction studies. Absolute stereochemistry was determined via hydrolysis of the amino sugar glycosidically linked to the aglycone, which was identified as L-kedarosamine. The overall three-dimensional structure is closely related to that of the macrolides cytovaricin, rutamycin, and ossamycin.

The stereochemical outcome of electrophilic addition reactions on the 5,6-double bond in the spinosyns.

The electrophilic addition of reagents to the 5,6-double bond in spinosyn A and spinosyn D systems occurred with high pi-diastereofacial selectivity. Addition occurred preferentially from the beta face of the molecule with selectivities ranging from 5:1 to better than 30:1. Various NMR properties were investigated in order to distinguish the beta and alpha isomers with the help of theoretical models of the products. These NMR properties include a (13)C gamma effect to C-11 and vicinal coupling between H-4 and H-5. To help rationalize the selectivity, computational studies on the transition states for epoxidation were calculated using density functional theory. The results indicate that beta epoxidation is favored and that the geometries of the transition structures are consistent with torsional steering being the source of the selectivity.

Antimicrobial characterization and interrelationships of dirithromycin and epidirithromycin.

Dirithromycin is the 9-N,11-O-oxazine adduct formed from 9(S)-erythromycylamine and 2-(2-methoxyethoxy)acetaldehyde in which the methoxyethoxymethyl substituent on the oxazine ring possesses the R configuration. Epidirithromycin is its isomer in which the methoxyethoxymethyl substituent has the opposite (S) configuration. Both compounds readily epimerize in solution, reaching an equilibrium ratio of 85:15 in favor of dirithromycin, given sufficient time. The rate of interconversion is dependent upon pH, temperature, and solvent. An enriched sample of epidirithromycin (95% purity) was synthesized by condensing erythromycylamine and 2-(2-methoxyethoxy)acetaldehyde in diethyl ether as the reaction solvent, and the product was fully characterized by nuclear magnetic resonance spectroscopy and high-pressure liquid chromatographic (HPLC) analysis. Both oxazine derivatives readily hydrolyze to erythromycylamine, so all three compounds exhibit the same antibiotic activity in vitro. In order to determine whether dirithromycin itself possesses significant antimicrobial activity without initial hydrolysis to erythromycylmine, inhibition of cell-free ribosomal protein synthesis was measured under conditions which were adapted to minimize hydrolysis, as measured by analytical HPLC in parallel experiments. Under these particular conditions, inhibition of ribosomal protein synthesis by dirithromycin was < 10% of the value measured for erythromycylamine.