Sanglifehrin-cyclophilin interaction: degradation work,synthetic macrocyclic analogues,X-ray crystal structure,and binding data

Sanglifehrin A (SFA) is a novel immunosuppressive natural product isolated from Streptomyces sp. A92-308110. SFA has a very strong affinity for cyclophilin A (IC(50) = 6.9 +/- 0.9 nM) but is structurally different from cyclosporin A (CsA) and exerts its immunosuppressive activity via a novel mechanism. SFA has a complex molecular structure consisting of a 22-membered macrocycle, bearing in position 23 a nine-carbon tether terminated by a highly substituted spirobicyclic moiety. Selective oxidative cleavage of the C(26)=C(27) exocyclic double bond affords the spirolactam containing fragment 1 and macrolide 2. The affinity of 2 for cyclophilin (IC(50) = 29 +/- 2.1 nM) is essentially identical to SFA, which indicates that the interaction between SFA and cyclophilin A is mediated exclusively by the macrocyclic portion of the molecule. This observation was confirmed by the X-ray crystal structure resolved at 2.1 A of cyclophilin A complexed to macrolide 16, a close analogue of 2. The X-ray crystal structure showed that macrolide 16 binds to the same deep hydrophobic pocket of cyclophilin A as CsA. Additional valuable details of the structure-activity relationship were obtained by two different chemical approaches: (1) degradation work on macrolide 2 or (2) synthesis of a library of macrolide analogues using the ring-closing metathesis reaction as the key step. Altogether, it appears that the complex macrocyclic fragment of SFA is a highly optimized combination of multiple functionalities including an (E,E)-diene, a short polypropionate fragment, and an unusual tripeptide unit, which together provide an extremely strong affinity for cyclophilin A.     

Combinatorial synthesis of natural product-like molecules using a first-generation spiroketal scaffold

Recently, significant attention has been focused on the synthesis small-molecule libraries based on natural product or natural product-like structures. In this paper, we report our initial studies on the use of the 1,7-dioxaspiro[5,5]undecane (spiroketal) moiety as a rigid-core template for elaboration using parallel synthesis techniques. The synthesis of a spiroketal scaffold that is reminiscent of the spiroketal subunits found in the spiroketal macrolide antibiotics will be described. Elaboration of three independently addressable functional groups on the scaffold using solution-phase parallel synthesis techniques led to the preparation of a small library of natural product-like compounds. These studies pave the way for evaluation of highly functionalized spiroketals in phenotypic assays and as prospective antagonists of protein-protein interactions.     

The stereoselective synthesis of novel macrolide antibacterial agents via an intramolecular 1,3-dipolar cycloaddition of azomethine ylide

An intramolecular 1,3-dipolar cycloaddition of azomethine ylide, generated in situ via the reaction of C12-glycinate derivative of macrolide with formaldehyde, provided a novel tricyclic macrolide. The high stereoselectivity of this [2+3] reaction was achieved by introducing a suitable directing group at C-6 position of macrolide.     

Probing the breadth of macrolide glycosyltransferases: in vitro remodeling of a polyketide antibiotic creates active bacterial uptake and enhances potency

The glycan portion of macrolide antibiotics modulates their efficacy. High-level expression of three macrolide GTs and kinetic analysis has revealed a highly selective synthetic "tool kit" with such plasticity that 12 glycan-modified macrolide antibiotics have been readily created. One of these (1-Gal) is enhanced over its parent oleandomycin (1) by "glycotargeting", allowing higher uptake through active internalization by virtue of the attachment of a glycan (Gal) not normally found on 1. Subsequent release of the targeting glycan by endogenous galactosidase activity releases 1.     

Synthesis of macrolides

The biologically important macrolide class of natural products, although known for some time, has until recently received little synthetic attention. This was primarily due to the lack of general synthetic methodology and the complex structures involved, but in recent years has changed with the development of new experimental techniques. The recent synthetic advancements in this area, reported from the laboratories of Prof. E.J. Corey of Harvard University were undoubtedly the most powerful single thrust that brought these medicinally useful molecules into focus and propelled them into the forefront of organic synthesis. Following a brief introduction into the macrolide structural spectrum, the general methodology for macrolide synthesis is discussed in detail with several illustrative applications. A number of total syntheses of macrolides is then detailed with particular emphasis on the key macrolide ring-forming reactions.     

Symbiodinolactone A,a new 12-membered macrolide from symbiotic marine dinoflagellate Symbiodinium sp.

A new 12-membered macrolide, symbiodinolactone A, was isolated from the culture broth of symbiotic marine dinoflagellate Symbiodinium sp. The gross structure of symbiodinolactone A was elucidated by spectroscopic analyses, and the relative configuration was elucidated by the J-based configuration analysis and density-functional theory calculations. Symbiodinolactone A is the new 12-membered macrolide possessing an E double bond between C-4 and C-5, a branched methyl group at C-7, and a 1,2,3-trihydroxybutyl group at C-11. Symbiodinolactone A is the first usual size macrolide and the first non-nitrogen-containing macrolide from dinoflagellate Symbiodinium sp. Symbiodinolactone A might be generated by the unexplained dinoflagellate polyketide biosynthetic machinery.     

A synthetic and in silico study on the highly regioselective Diels-Alder reaction of the polyenic antifungal antibiotics natamycin and flavofungin

The tetraenic macrolide antibiotic natamycin and the pentaenic macrolide flavofungin gave monoadducts on Diels-Alder reaction with 4-phenyl-1,2,4-triazoline-3,5-dione. The regioselectivity of the reaction as well as the conformation of the products was studied using theoretical calculations.     

Neaumycin: a new macrolide from Streptomyces sp. NEAU-x211

Neaumycin, a new 30-membered macrolide featuring an internal diester bridge, a molecular architecture that is unprecedented among known macrolide natural products, was isolated from a soil actinomycete strain Streptomyces sp. NEAU-x211. The structure of neaumycin was elucidated on the basis of comprehensive mass and NMR spectroscopic interpretation, including the relative stereochemistry of four independent coupling systems.     

Rapid entry into the cryptophycin core via an acyl-beta-lactam macrolactonization: total synthesis of cryptophycin-24

[see structure]. An efficient, concise approach to the macrolide core of the cryptophycins, potent antimitotic agents, has been achieved. The reaction sequence features a novel macrolactonization utilizing a reactive acyl-beta-lactam intermediate that incorporates the beta-amino acid moiety within the 16-membered macrolide core. This highly modular approach, which allows for multiple alterations throughout the structure, was successfully applied to the total synthesis of cryptophycin-24.     

A comparative uncertainty study of the calibration of macrolide antibiotic reference standards using quantitative nuclear magnetic resonance and mass balance methods

This study introduces the general method of quantitative nuclear magnetic resonance (qNMR) for the calibration of reference standards of macrolide antibiotics. Several qNMR experimental conditions were optimized including delay, which is an important parameter of quantification. Three kinds of macrolide antibiotics were used to validate the accuracy of the qNMR method by comparison with the results obtained by the high performance liquid chromatography (HPLC) method. The purities of five common reference standards of macrolide antibiotics were measured by the ¹H qNMR method and the mass balance method, respectively. The analysis results of the two methods were compared. The qNMR is quick and simple to use. In a new medicine research and development process, qNMR provides a new and reliable method for purity analysis of the reference standard.     

Total synthesis of bafilomycin A(1) relying on iterative 1,2-induction in acyclic precursors

The macrolide bafilomycin A(1) was synthesized starting from D-valine and D-mannitol as chiral progenitors of propionate units. Acyclic subunits corresponding to different parts of the molecule were constructed based on an iterative 1,2-asymmetric induction protocol as a distinctive feature of the synthesis. The assembly of two segments encompassing the entire carbon framework of the macrolide was achieved by using a Stille coupling. The resulting seco-ester was further manipulated to provide crystalline bafilomycin A(1) via a conventional carbodiimide-mediated Keck-type macrolactonization.     

Characterization of tylM3/tylM2 and mydC/mycB pairs required for efficient glycosyltransfer in macrolide antibiotic biosynthesis

The heterologous expression of tylM3 and mydC, two homologous genes of previously unknown function, along with genes encoding their respective partner glycosyltransferases, tylM2 and mycB, and the necessary sugar biosynthesis genes significantly enhances the glycosyltransferase activity in the engineered Streptomyces venezuelae host in which the native glycosyltransferase, desVII, has been inactivated. Both glycosyltransferases accept the endogenous 12-membered macrolide, 10-deoxymethynolide, or the exogenously fed 16-membered macrolide, tylactone. Five new compounds were generated using this expression system. This work suggests that the 13 other known TylM3/MydC/DesVIII homologues found in macrolide and anthracycline antibiotic clusters likely function as glycosyltransferase auxiliary proteins as well. These findings will greatly assist endeavors to generate new natural products in these pathways in a combinatorial fashion.     

蜂王浆产品中5种大环内酯类抗生素残留量的高效液相色谱-质谱/质谱检测方法

建立了高效液相色谱-质谱/质谱测定蜂王浆中5种大环内酯类抗生素(螺旋霉素、竹桃霉素、泰乐菌素、罗红霉素、交沙霉素)残留的方法。先用三氯乙酸沉淀蜂王浆中的蛋白质,上层清液再用乙腈提取、C18小柱净化。每种抗生素选择一个母离子和两个子离子进行监测。5种大环内酯类抗生素在0.002～0.05 mg/L 范围内与其峰面积具有良好的线性关系,检测低限均为20 μg/kg,3个加标水平（每种抗生素的添加水平均为20, 100 和 200 μg/kg）下的加标回收率为73.0%～90.2%,相对标准偏差为5.6%～10.5%。     

Total synthesis of pikromycin

The total synthesis of pikromycin (6), the first isolated macrolide antibiotic, was achieved. The target macrolide was retrosynthetically divided into two parts, pikronolide (6a) (aglycon) and D-desosamine. The aglycon was synthesized using key reactions such as an asymmetric aldol reaction, Yamaguchi esterification, and ring-closing metathesis. The aglycon was coupled successfully with the trichloroacetimidate derivative of D-desosamine under Lewis acidic conditions to afford pikromycin. Narbomycin (5) was also synthesized from narbonolide (5a) under identical conditions.     

Biosynthesis of desosamine: construction of a new macrolide carrying a genetically designed sugar moiety

[formula: see text] The appended sugars in macrolide antibiotics are indispensable to the biological activities of these important drugs. In an effort to generate a set of novel macrolide derivatives, we have created a new analogue of methymycin and neomethymycin, antibiotics produced by Streptomyces venezuelae. This analogue 15 carrying a different sugar, D-quinovose, instead of D-desosamine, was constructed by taking advantage of targeted gene deletion combined with a specific pathway-independent C-3 reduction capability of the wild type S. venezuelae.     

Determination of Dirithromycin,LY281389 and Other Macrolide Antibiotics by HPLC with Electrochemical Detection

Abstract

Sensitive and rapid assays have been developed for the determination of the macrolide antibotics dirithromycin, erythromycylamine, and LY281389 in plasma. The methods utilize dichloromethane extraction of alkalinized plasma and isocratic reverse phase HPLC with electrochemical detection. The lower limit of detection is 10 ng/ml. Calibration curves are linear and highly reproducible over the range of 20–500 ng/ml. Precision of the calibration curves is very good having relative standard deviations of 5% or less over the dynamic range. These methods can be used for other macrolide antibiotics with minor modifications to the mobile phase. The electrochemical response of various macrolides was found to be dependent upon the functionality at C-9 of the macrolide ring.     

Concise Synthesis and Biological Assessment of (+)‐Neopeltolide and a 16‐Member Stereoisomer Library of 8,9‐Dehydroneopeltolide: Identification of Pharmacophoric Elements

We describe herein a concise synthesis of (+)‐neopeltolide, a marine macrolide natural product that elicits a highly potent antiproliferative activity against several human cancer cell lines. Our synthesis exploited the powerful bond‐forming ability and high functional group compatibility of olefin metathesis and esterification reactions to minimize manipulations of oxygen functionalities and to maximize synthetic convergency. Our findings include a chemoselective olefin cross‐metathesis reaction directed by H‐bonding, and a ring‐closing metathesis conducted under non‐high dilution conditions. Moreover, we developed a 16‐member stereoisomer library of 8,9‐dehydroneopeltolide to systematically explore the stereostructure–activity relationships. Assessment of the antiproliferative activity of the stereoisomers against A549 human lung adenocarcinoma, MCF‐7 human breast adenocarcinoma, HT‐1080 human fibrosarcoma, and P388 murine leukemia cell lines has revealed marked differences in potency between the stereoisomers. This study provides comprehensive insights into the structure–activity relationship of this important antiproliferative agent, leading to the identification of the pharmacophoric structural elements and the development of truncated analogues with nanomolar potency.     

A total synthesis of the antitumour macrolide rhizoxin D

An enantioselective synthesis of rhizoxin D, isolated from the plant pathogenic fungus Rhizopus chinensis, is described. The overall strategy is based on elaboration of the delta-lactone-substituted vinyl stannane and the phosphonate-substituted vinyl iodide, followed by their coupling to the core 16-membered macrolide via a sequential intermolecular Horner-Wadsworth-Emmons olefination, leading to (50), and by an intramolecular Stille reaction. The triene oxazole-containing side chain in rhizoxin D is then introduced using the phosphine oxide in an E-selective Horner-Wittig reaction with the macrolide aldehyde.     

Amphidinolide W, a new 12-membered macrolide from dinoflagellate Amphidinium sp

A new cytotoxic 12-membered macrolide, amphidinolide W (1), has been isolated from a marine dinoflagellate Amphidinium sp., and the structure was elucidated by spectroscopic data including (13)C-(13)C INADEQUATE correlations for its (13)C-enriched sample. The absolute stereochemistry of 1 was assigned by combination of J-based configuration analysis and modified Mosher method. Amphidinolide W (1) is the first macrolide without an exomethylene unit among all amphidinolides obtained so far.     

Macrolides. Recent Progress in Chemistry and Biochemistry

The progress of macrolide chemistry and biochemistry over the past several years has indeed been remarkable. This review attempts to cover the important contributions which have been made in the fields of structural and synthetic chemistry as well as in the biosynthesis and mode of antimicrobial activity of the “polyoxo” macrolide antibiotics. Emphasis has been placed on the recent synthetic achievements in this field.