isomigrastatin and migrastatin

Migrastatin and isomigrastatin analogues have been synthesised in order to contribute to structure-activity studies on tumour cell migration inhibitors. These include macrocycles varying in ring size, functionality and alkene stereochemistry, as well as glucuronides. The synthesis work included application of the Saegusa-Ito reaction for regio- and stereoselective unsaturated macroketone formation, diastereoselective Brown allylation to generate 9-methylmigrastatin analogues and chelation-induced anomerisation to vary glucuronide configuration. Compounds were tested in vitro against both breast and pancreatic cancer cell lines and inhibition of tumour cell migration was observed in both wound-healing (scratch) and Boyden chamber assays. One unsaturated macroketone showed low affinity for a range of secondary drug targets, indicating it is at low risk of displaying adverse side effects.

Topics: Alkenes; Cell Line, Tumor; Cell Movement; Female; Glucuronides; Humans; Macrocyclic Compounds; Macrolides; Pancreatic Neoplasms; Piperidones; Structure-Activity Relationship

iso-Migrastatin and related glutarimide-containing polyketides are potent inhibitors of tumor cell migration and their implied potential as antimetastatic agents for human cancers has garnered significant attention. Genome scanning of Streptomyces platensis NRRL 18993 unveiled two candidate gene clusters (088D and mgs); each encodes acyltransferase-less type I polyketide synthases commensurate with iso-migrastatin biosynthesis. Both clusters were inactivated by lambda-RED-mediated PCR-targeting mutagenesis in S. platensis; iso-migrastatin production was completely abolished in the DeltamgsF mutant SB11012 strain, whereas inactivation of 088D-orf7 yielded the SB11006 strain that exhibited no discernible change in iso-migrastatin biosynthesis. These data indicate that iso-migrastatin production is governed by the mgs cluster. Systematic gene inactivation allowed determination of the precise boundaries of the mgs cluster and the essentiality of the genes within the mgs cluster in iso-migrastatin production. The mgs cluster consists of 11 open reading frames that encode three acyltransferase-less type I polyketide synthases (MgsEFG), one discrete acyltransferase (MgsH), a type II thioesterase (MgsB), three post-PKS tailoring enzymes (MgsIJK), two glutarimide biosynthesis enzymes (MgsCD), and one regulatory protein (MgsA). A model for iso-migrastatin biosynthesis is proposed based on functional assignments derived from bioinformatics and is further supported by the results of in vivo gene inactivation experiments.

Topics: Base Sequence; Gene Deletion; Genome, Bacterial; Macrolides; Molecular Sequence Data; Multigene Family; Open Reading Frames; Piperidones; Polyketide Synthases; Streptomyces

Thermolysis of isomigrastatin (1) under neat heating conditions afforded migrastatin (1a). The reaction is proposed to proceed via a concerted [3,3]-sigmatropic rearrangement by which ring expansion is achieved regio- and enantiospecifically. The general applicability of this reaction was demonstrated with six additional isomigrastatin congeners (3-8), providing a new route to the synthesis of migrastatin analogues (3a-8a). [reaction: see text]

Topics: Chromatography, High Pressure Liquid; Hot Temperature; Isomerism; Lactones; Macrolides; Magnetic Resonance Spectroscopy; Mass Spectrometry; Piperidones; Stereoisomerism

Fermentation of Streptomyces platensis NRRL18993 typically accumulated migrastation (1), dorrigocin A (2) and B (3), and 13-epi-dorrigocin A (5). Supplement of XAD-16 resin to the fermentation, in contrast, resulted in exclusive production of iso-migrastatin (4). In vitro studies showed that 1, 2, 3, and 5 are stable in aqueous solution but 4 undergoes rapid conversion into 1, 2, 3, and 5 under the same condition. These results revealed that 4 is the only bona fide natural product biosynthesized by S. platensis, and 1, 2, 3, and 5 are shunt metabolites of 4. This study also established the stereochemistry of 2-5 with the exception of C-11 for 3 and 4. A mechanism for H2O-mediated regio- and stereospecific rearrangement of 4 to 1, 2, 3, and 5 is proposed and supported by incorporation of 18O from H218O.

Topics: Chromatography, High Pressure Liquid; Lactones; Macrolides; Piperidones; Spectrometry, Mass, Electrospray Ionization; Stereoisomerism; Streptomyces

Streptomyces platensis (strain NRRL 18993), a producer of dorrigocins, was shown to produce migrastatin, a cyclic congener of dorrigocin A previously reported from a different organism. Additionally a new compound isomeric to migrastatin, isomigrastatin, was also isolated and its structure was determined to be a cyclic form of dorrigocin B. Both compounds were fully characterized from MS and NMR data. Product titers of both were improved by the addition of XAD-16 resin to the fermentation medium.

Topics: Antibiotics, Antineoplastic; Fermentation; Lactones; Macrolides; Molecular Structure; Piperidones