Biomedical subjects

David F Wiemer

Publications and source records attributed to David F Wiemer.

16 recordsLinked to original sources

PubMed2006

Synthesis and biological activity of isoprenoid bisphosphonates.

Bisphosphonates have been used in the clinic to treat osteoporosis and to reduce bone resorption and the accompanying pathological bone fractures that attend a number of malignancies including multiple myeloma and cancers of the prostate, breast, and lung. There is also evidence that some bisphosphonates have direct anticancer activity. Expansion of the current class of bisphosphonates may lead to compounds that more selectively and potently target these cancers through inhibition of the mevalonate pathway. To this end, a set of dialkyl bisphosphonates bearing isoprenoid chains of varying lengths has been synthesized. Some of these compounds were found to have biological activity on post-translational processing of the oncogenic small GTPases, Ras and Rap1a, in human-derived K562 leukemia cells. Most importantly, these compounds impair protein geranylgeranylation and not protein farnesylation.

Cell Line↗

PubMed2005

Synthesis and structure-activity studies of schweinfurthin B analogs: Evidence for the importance of a D-ring hydrogen bond donor in expression of differential cytotoxicity.

The synthesis and biological evaluation of several enantioenriched schweinfurthin B analogs were undertaken to develop structure-activity relationships and guide design of probes for their putative molecular target. The desired stilbenes contain a common left-half hexahydroxanthene ring system and an aromatic right-half with varied substituents. The synthesis involves penultimate Horner-Wadsworth-Emmons coupling of one of several right-half phosphonates with the aldehyde comprising the left-half of 3-deoxyschweinfurthin B. Preparation of the requisite phosphonates, and the respective stilbenes, as well as the cytotoxicity profiles of these new compounds in the National Cancer Institute's 60 cell-line anticancer screen is described. Several of these analogs displayed cytotoxicity patterns well-correlated with the natural product and differences in activity of approximately 10(3) across the various cell lines. Together, these assay results indicate the importance of at least one free phenol group on the aromatic D-ring of this system for differential cytotoxicity.

Cell Line, Tumor↗

PubMed2005

Synthesis of farnesol isomers via a modified Wittig procedure.

[structure: see text] The four olefin stereoisomers of farnesol have been synthesized from readily available nerylacetone or commercial geranylacetone. A new variation on the use of beta-oxido ylides favored the (2Z)-stereoisomers, whereas the (2E)-isomers were obtained through a classical Horner-Wadsworth-Emmons condensation with triethyl phosphonoacetate and reduction of the resulting ester.

Chemistry, Organic↗

PubMed2005

Synthesis of nonracemic 3-deoxyschweinfurthin B.

Synthesis of nonracemic 3-deoxyschweinfurthin B has been accomplished through a synthetic sequence including a key cascade cyclization of an epoxy olefin. The intermediate epoxide could be prepared as a single enantiomer through an AD-mix-alpha (or AD-mix-beta) oxidation, and the stereochemistry of the epoxide has been shown to control formation of the two additional stereogenic centers created through the cyclization. Synthetic 3-deoxyschweinfurthin B was found to have potent differential activity in the National Cancer Institute's 60 cell line anticancer assay. This represents the first synthesis of the tetracyclic schweinfurthin skeleton, validating our overall synthetic strategy and providing the first schweinfurthin analogue with activity slightly greater than those of the natural products.

Antineoplastic Agents↗

PubMed2005

Synthesis of arieianal, a prenylated benzoic acid from Piper arieianum.

Arieianal (1) is a complex prenylated benzoic acid that was isolated from Piper arieianum. It has been synthesized through a convergent sequence that joins a functionalized diterpenoid chain to a protected aromatic core. Key steps include use of a copper enolate for selective displacement of an allylic bromide in the presence of an allylic acetate and a stereoselective Horner-Wadsworth-Emmons condensation to afford the desired E olefin of the isoprenoid side chain. After the diterpenoid chain was joined to the aromatic ring, use of sodium metal in hot sBuOH allowed selective cleavage of two benzyl ether protecting groups, and a sequence of oxidations gave the target compound. This synthesis confirms the structure assigned to the natural product and establishes a route that may be used to prepare more active analogues.

Benzoates↗

PubMed2004

Synthesis and activity of fluorescent isoprenoid pyrophosphate analogues.

New fluorescent analogues of farnesol and geranylgeraniol have been prepared and then converted to the corresponding pyrophosphates. These analogues incorporate anthranylate or dansyl-like groups anchored to the terpenoid skeleton through amine bonds that would be expected to be relatively stable to metabolism. After addition of the alcohols or the pyrophosphates to the culture medium, their fluorescence is readily observed inside a human-derived leukemia cell line. Enzyme assays have revealed that the farnesyl pyrophosphate analogue is an inhibitor of FTase, while the corresponding alcohol is not. These results, together with Western blot analyses of cell lysates, indicate that the farnesyl pyrophosphate analogue penetrates the cells as an intact pyrophosphate and that it does so at a biologically relevant concentration.

Cell Line, Tumor↗

PubMed2003

Alpha-phosphono lactone analogues of cytidine and cytosine arabinoside diphosphates: synthesis via ring closing metathesis.

alpha-Phosphono lactone derivatives of the nucleosides cytidine and cytosine arabinoside have been prepared from the corresponding nucleoside aldehydes. The stereochemical outcome of allylation reactions with these aldehydes was found to be dependent upon both the choice of protecting groups for the 2'- and 3'-hydroxyl groups and, to some extent, the nature of the Lewis acid catalyst employed. Ultimately, conditions were found that favored either the 5'R or 5'S diastereomer from different cytidine aldehydes, and gave some stereoselectivity in additions to an aldehyde derivative of ara-C. The resulting homoallylic alcohols were used as substrates in attempted Knovenagel and Horner-Wadsworth-Emmons condensations, but elimination was found to predominate over lactone formation under the conditions employed. The desired alpha-phosphono lactones could be prepared through a reaction sequence that included ring-closing metathesis on acrylate esters of the homoallylic alcohols, followed by reduction of the resulting alpha,beta-unsaturated lactones and carbon-phosphorus bond formation on enolates generated from the saturated lactones.

Arabinose↗

PubMed2003

Synthesis of 5'-amino-5'-phosphonate analogues of pyrimidine nucleoside monophosphates.

The 5'-amino-5'-phosphono derivatives of cytidine, cytosine arabinoside (ara-C), and uridine have been prepared via the corresponding nucleoside aldehydes. Phosphite addition to imines derived from the nucleoside aldehydes and p-methoxybenzylamine was efficient, and use of this amine allowed cleavage of the products to the parent amino phosphonic acids. The phosphite additions proved to be diastereoselective, with the cytidine and uridine derivatives favoring the 5'S stereochemistry and the ara-C derivative favoring the 5'R isomer. The stereochemistry of one cytidine derivative was established by single-crystal diffraction analysis, and detailed comparisons of the (13)C NMR data allowed assignments of the other amino phosphonates.

Chromatography, Thin Layer↗

PubMed2003

Tripeptide probes for tripeptidyl protease I production via gene transfer.

Tripeptides derived from 5-chloroanthraquinone hydrazide and anthraquinone hydrazide have been prepared as potential reagents to probe cellular expression of tripeptidyl protease I (TPP-I). Attempted chemical synthesis of Gly-l-Pro-l-Ala-chloroanthraquinone hydrazide, a compound that had been reported to serve as a substrate for this enzyme, was complicated by formation of a pyrazoloquinone. In contrast, formation of pyrazoloquinones was not observed during coupling reactions with anthraquinone hydrazide, and several tripeptide derivatives of this compound were prepared. The most attractive probe for TPP-I activity in tests with mouse kidney tissue sections proved to be Gly-l-Pro-l-Ser anthraquinone hydrazide.

Aminopeptidases↗

PubMed2003

Isoprenoid pyrophosphate analogues regulate expression of Ras-related proteins.

The isoprenoids farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) are synthetic precursors for numerous molecules essential for cellular function as well as substrates in isoprenylation reactions. We have previously demonstrated that depletion of mevalonate results in the upregulation of Ras-related proteins which can be prevented by FPP or GGPP, independent of restoration of protein isoprenylation. To better define the regulatory properties of isoprenoid pyrophosphates, we have investigated the abilities of isoprenoid analogues to regulate the expression of the Ras-related proteins. Farnesyl phosphonic acids potentiate the upregulation of these proteins induced by mevalonate depletion independent of inhibitory activity against farnesyl protein transferase, geranylgeranyl protein transferase I, FPP synthase, or GGPP synthase. The potentiation of RhoB upregulation is at both the mRNA and protein level. The ability of these analogues to serve as functional antagonists of the isoprenoid pyrophosphates is dependent on the nature of the functional group at the head of the molecule, the charge of the molecule, and the length of the isoprenoid chain. Metabolites and additional analogues of isoprenoid pyrophosphates were found to possess agonist properties relative to FPP and GGPP. Interestingly, the structurally related retinoids all-trans-retinoic acid and 9-cis-retinoic acid also display slight agonist properties. These studies provide evidence for direct roles of FPP and GGPP in regulating transcriptional and post-transcriptional events.

Diphosphates↗

PubMed2002

Stereoselective synthesis of the 5'-hydroxy-5'-phosphonate derivatives of cytidine and cytosine arabinoside.

Both the (R)- and (S)-5'-hydroxy 5'-phosphonate derivatives of cytidine and cytosine arabinoside (ara-C) have been prepared via phosphite addition or a Lewis acid mediated hydrophosphonylation of appropriately protected 5'-nucleoside aldehydes. Phosphite addition to a cytosine aldehyde protected as the 2',3'-acetonide gave predominately the 5'R isomer, while phosphite addition to the corresponding 2',3'-bis TBS derivative favored the 5'S stereochemistry. In contrast, phosphite addition to the 2',3'-bis TBS protected aldehyde derived from ara-C gave only the 5'R adduct. However, TiCl(4)-mediated hydrophosphonylation of the same ara-C aldehyde favored the 5'S stereoisomer by a 2:1 ratio. Once all four of the diastereomers were in hand, the stereochemistry of these compounds could be assigned based on their spectral data or that obtained from their O-methyl mandelate derivatives. After hydrolysis of the phosphonate esters and various protecting groups, the four alpha-hydroxy phosphonic acids were tested for their ability to serve as substrates for the enzyme nucleoside monophosphate kinase and for their toxicity to K562 cells.

Cytarabine↗

PubMed2002

Synthesis of a carbon analogue of N-acetylmannosamine via acetolysis on a relatively stable ozonide.

After a 2-methylpropenyl group was added to a carbohydrate framework through regioselective opening of a glucose-derived epoxide, hydrolysis or acetolysis of the methyl glycoside in various derivatives was problematic. Ozonolysis of the olefin followed by brief treatment with dimethyl sulfide gave a mixture of diastereomeric ozonides that proved to be stable for weeks at room temperature. Acetolysis of these ozonides at low temperature allowed selective cleavage of the methyl glycoside in the presence of the 1,2,4-trioxolane as well as selective formation of the alpha-acetate.

Acetates↗

PubMed2002

A cascade cyclization approach to schweinfurthin B.

[reaction: see text] A strategy for synthesis of the hexahydroxanthene moiety of the natural products schweinfurthin A, B, and D is described. The relative stereochemistry in the key cationic cyclization step is established through the preference of the phenylselenide substituent for an equatorial orientation.

Magnetic Resonance Spectroscopy↗

PubMed2002

Chiral liquid chromatography separation and chiroptical properties of the enantiomers of dimethyl alpha-hydroxyfarnesylphosphonate, a precursor of a farnesyl protein transferase inhibitor.

The HPLC enantiomeric separation of racemic and non-racemic samples of dimethyl alpha-hydroxyfarnesylphosphonate (1) was accomplished using Chiralcel OD as chiral stationary phase. Single enantiomers were isolated by semipreparative HPLC and their CD spectra and optical rotations were measured. The method ascertains enantiomeric excess of 1, obtained by oxidation of dimethylfarnesylphosphonate with enantiopure oxaziridines, avoiding converting the enantiomers to diastereomers by the use of a chiral auxiliary. Stability of the solutions of 1 is strongly dependent on the nature of the solvent.

Chromatography, High Pressure Liquid↗

PubMed2002

Preparation of alpha-phosphono lactams via electrophilic phosphorus reagents: an application in the synthesis of lactam-based farnesyl transferase Inhibitors.

Conversion of N-alkyl lactams to the corresponding alpha-phosphono lactams has been investigated through procedures that involve formation of the lactam enolate and reaction with a phosphorus electrophile. With N-octylpyrrolidinone, the enolate could be trapped efficiently on oxygen by reaction with diethyl phosphorochloridate, and the resulting vinyl phosphate rearranges smoothly to the desired phosphonate upon treatment with additional LDA. Attempts to apply the same protocol to N-farnesyl lactams met with limited success. Studies with an isolated alpha-phosphono N-farnesyl lactam have shown that the farnesyl group is not stable to the excess of strong base required for rearrangement of a vinyl phosphate. However, a series of N-farnesyl lactams and imides was converted to the desired phosphonates through formation of the lactam enolate, reaction with diethyl phosphorochloridite, and subsequent oxidation of the phosphorus intermediate to the P(V) state.

Alkyl and Aryl Transferases↗

PubMed2002

Alpha-phosphono lactone analogues of farnesyl pyrophosphate: an asymmetric synthesis via ring-closing metathesis.

An alpha-phosphono lactone derivative of farnesol has been prepared, in both racemic and nonracemic forms, to provide a new type of farnesyl pyrophosphate analogue. Attempted preparation of the racemic alpha-phosphono lactone through rearrangement of a vinyl phosphate derived from the parent lactone resulted in both rearrangement and lactone ring opening, revealing that the farnesyl lactone was not stable to the excess of strong base required for the rearrangement. A procedure for C-P bond formation based on generation of the lactone enolate, reaction with a P(III) reagent, and oxidation was successful in providing the racemic alpha-phosphono lactone, in part, because only 1 equiv of strong base was required. The same strategy for phosphonate synthesis then was applied to the nonracemic farnesyl lactone, prepared through a sequence including allylation of farnesal with a nonracemic borane reagent, reaction of the product alcohol with acryloyl chloride, and formation of an unsaturated lactone through ring-closing metathesis. A similar strategy gave the corresponding racemic alpha-phosphono lactam through a six-step sequence from farnesal.

Ether↗