Total synthesis and structural revision of (+)-amphidinolide W

An enantioselective first total syntheis of amphidinolide W (2) and a revision of its C6 absolute stereochemistry (1) are described. Amphidinolide W (1), a 12-membered macrolide isolated from Amphidinium sp., has shown potent antitumor properties against a variety of NCI tumor cell lines. The synthesis is convergent, and four of the five chiral centers were derived through asymmetric synthesis. The synthesis features Sharpless asymmetric dihydroxylation, diastereoselective alkylation, efficient cross metathesis of functionalized substrates, and novel functional group transformations using selective lipase-catalyzed hydrolysis of the primary acetate group. Of particular note, the C6 absolute stereochemistry of amphidinolide W (1) has now been revised through our current synthesis.     

Biosynthetic study of amphidinolide B

The biosynthetic origins of amphidinoide B (1) were investigated on the basis of 13C-NMR data of 13C-enriched samples obtained by feeding experiments with [1-(13)C], [2-(13)C], and [1,2-(13)C2] sodium acetates in cultures of a dinoflagellate Amphidinium sp. These incorporation patterns suggested that 1 was generated from three successive polyketide chains, an isolated C1 unit from C-2 of acetates, six branched C1 units from C-2 of acetates, and an "m-m" and an "m-m-m" unit derived only from C-2 of acetates. The labeling patterns of amphidinolide B (1) were different from those of amphidinolide H (2), a 26-membered macrolide closely related to 1.     

Relative Configuration of JBIR-129, a Cytotoxic 34-Membered Glycosidic Polyol Macrolide from Streptomyces sp. RK74

JBIR-129 was isolated as the potent cytotoxic compound, which consists of the 34-membered polyol macrolide skeleton with five sugar moieties. The relative configuration of the aglycone moiety (C7-C27 and C33-C39) was established by the J-based configuration analysis using vicinal (1)H-(1)H (from (1)H NMR and PS-DQF-COSY spectra) and long-range (1)H-(13)C coupling constants (from sge-HETLOC and several J-resolved HMBC spectra) with steric information obtained from ROESY.     

Structure elucidation,complete NMR assignment and PM5 theoretical studies of new hydroxy‐aminoalkyl‐α,β‐unsaturated derivatives of the macrolide antibiotic josamycin

Four new hydroxy‐aminoalkyl derivatives of α,β‐unsaturated macrolide‐josamycin (2–5) have been synthesised and their structures have been studied by means of ¹H and ¹³C NMR and FT‐IR methods. Complete assignment of resonances in the ¹H and ¹³C NMR spectra has been made on the basis of ¹H? ¹³C HSQC, ¹H? ¹³C HMBC, ¹H? ¹H COSY, ¹H? ¹H NOESY 2D experiments. Spectroscopic data indicated that for the derivatives 3 and 4 some equilibrium between two different structures exists in contrast to derivatives 2 and 5. The lowest‐energy structures of the new derivatives of josamycin have been calculated and visualised by PM5 method at semi‐empirical level of theory, taking into account the NMR and FT‐IR data. The most significant differences between the structures of josamycin and its newly synthesised derivatives' were found in the conformation of the macrolide aglycone part and in the mutual orientation of the 4‐O‐isovalerylmycarosylmycaminose moiety relative to the aglycone part. PM5 semi‐empirical calculations indicated that the structures of the new macrolide derivatives are stabilised by rather weak intramolecular hydrogen bonds in agreement with spectroscopic data. Antimicrobial properties of the new derivatives 2–5 as well as those having an acetate group at C‐3 (6 and 7) were determined and compared to that of the parent macrolide antibiotic josamycin (1). Copyright © 2010 John Wiley & Sons, Ltd.     

The unexpected isolation of CTP-431, a novel thiopyrone from the sponge Cacospongia mycofijiensis

A reinvestigation of a Fijian collection of Cacospongia mycofijiensis has yielded the known mycothiazole and a novel heterocyclic, CTP-431 (1). Its structure including absolute configuration as 8R,9R,10S,13S was established using NMR data, calculated DFT (13)C chemical shifts and results from X-ray crystallography. It is possible that the tricyclic skeleton of CTP-431 (1) is biosynthetically related to the macrolide latrunculin A, however the thiopyrone moiety of 1 has no previous precedent in natural products chemistry.     

Secondary Metabolites and Antifungal Activity of the Endophytic Fungus Streptomyces humidus SCB0232 from Water Chestnut

Chemistry of Natural Compounds - A new macrolide, named concanamycin H (1), together with 12 known compounds (2–13), was isolated from the endophytic Streptomyces humidus SCB0232 for the...     

Highly stereoselective synthesis of methynolide,the aglycone of the 12-membered ring macrolide methymycin,from D-glucose

A highly stereoselective and efficient synthesis of methynolide, the aglycone of 12-membered macrolide methymycin, was achieved from of C1–C8 and C9–C13 segments synthesized from D-glucose by employing some stereoselective reactions and benzyl-type protecting groups.     

Amphidinolide Y, a novel 17-membered macrolide from dinoflagellate Amphidinium sp.: plausible biogenetic precursor of amphidinolide X

A novel cytotoxic 17-membered macrolide, amphidinolide Y (1), has been isolated from a marine dinoflagellate Amphidinium sp., and it was elucidated to exist as a 9:1 equilibrium mixture of 6-keto- and 6(9)-hemiacetal forms (1a and 1b, respectively) on the basis of 2D NMR data and chemical means. The feeding experiments with (13)C-labeled acetates suggested that amphidinolide Y (1) may be a biogenetic precursor of 16-membered macrodiolide, amphidinolide X (2).     

Studies in macrolide synthesis: A highly stereoselective synthesis of (+)-(9S)-dihydroerythronolide a using macrocyclic stereocontrol

(+)-(9S)-Dihydroerythronolide A, 1, is prepared in 8 steps from macrolide 3 by exploiting the conformational preferences of the (5E,11E)-diene intermediate 2. The stereocontrolled introduction of the hydroxyl groups at C₆, C₁₁, and C₁₂ is achieved by osmylation, 2 → 13 and 15 → 1, while that at C₅ is obtained by a Zn(BH₄)₂ reduction, 13 → 14.     

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.     

Complete assignments of (1)H and (13)C NMR data for two 3beta,8beta-epoxymexicanolides from the fruit of a Chinese mangrove Xylocarpus granatum

Three 3beta,8beta-epoxymexicanolides, including xyloccensin K, 6-acetoxycedrodorin and a new one named xyloccensin W, were isolated from the fruit of a Chinese mangrove Xylocarpus granatum. Their structures were determined by spectroscopic analyses. The first complete assignment of (1)H and (13)C NMR data for xyloccensin W was achieved by means of 2D NMR techniques, including (1)H-(1)H COSY, HSQC, HMBC and NOESY spectra. In addition, the confusion of (1)H and (13)C NMR data previously reported for xyloccensin K was clarified.     

Total synthesis of (+)-13-deoxytedanolide

In this communication we describe the first total synthesis of (+)-13-deoxytedanolide, an architecturally complex marine macrolide possessing significant antitumor activity. The cornerstone of the synthesis comprises a highly convergent dithiane coupling used to construct the carbon skeleton, followed by a novel use of the Evans-Tishchenko reduction to oxidize the C(1) aldehyde to an ester in the presence of the oxidatively labile dithiane.     

Isolation and structure of koshikalide,a 14-membered macrolide from the marine cyanobacterium Lyngbya sp.

A 14-membered macrolide, koshikalide (1), was isolated from the marine cyanobacterium Lyngbya sp., and its planar structure was elucidated by spectroscopic analysis. The relative stereochemistry of C-11 and C-13 was elucidated by NOESY experiments and by an analysis of ¹H–¹H coupling constants. Koshikalide (1) exhibited weak cytotoxicity against HeLa S₃ cells.     

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.     

The first total synthesis of concanamycin f (concanolide a)

A highly stereoselective total synthesis of the macrolide antibiotic concanamycin F (1), a specific and potent inhibitor of vacuolar H(+)-ATPase, has been achieved by a convergent route involving the synthesis and coupling of its 18-membered tetraenic lactone and beta-hydroxyl hemiacetal side chain subunits. The C1-C19 18-membered lactone aldehyde 4 was synthesized through the intermolecular Stille coupling of the C5-C13 vinyl iodide 24 and the C14-C19 vinyl stannane 25, followed by construction of the C1-C4 diene and macrolactonization. Synthesis of 4 via a second convergent route including the esterification of the C1-C13 vinyl iodide 45 and the C14-C19 vinyl stannane 47 followed by the intramolecular Stille coupling was also realized. The highly stereoselective aldol coupling of 4 and the C20-C28 ethyl ketone 5 followed by desilylation provided 1 which was identical with natural concanamycin F.     

Amphidinolide T, novel 19-membered macrolide from marine dinoflagellate Amphidinium sp

A novel 19-membered macrolide, amphidinolide T (1), has been isolated from a marine dinoflagellate Amphidinium sp., and the structure was elucidated on the basis of spectroscopic data. Relative stereochemistry at C-7, C-8, and C-10 was deduced from the NOESY correlations, while absolute configurations at C-2, C-13, C-14, and C-18 were assigned on the basis of NMR data of the MTPA esters of 1 and those of degradation products of 1.     

Absolute stereochemistry of amphidinolide E

The absolute configurations at eight chiral centers in amphidinolide E (1), a cytotoxic 19-membered macrolide isolated from a marine dinoflagellate Amphidinium sp., were determined to be 2R, 7R, 8R, 13S, 16S, 17R, 18R, and 19R on the basis of detailed analysis of NMR data and by chemical means.     

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.     

18O assisted analysis of a γ,δ-epoxyketone cyclization: synthesis of the C16-C28 fragment of ammocidin D

The C16-C28 fragment common to the cytotoxic macrolide ammocidin D has been prepared by a stereospecific 5-exo closure of a γ,δ-epoxyketone followed by a rearrangement to a pyran acetal. The reaction pathway was traced by (18)O labeling of the keto carbonyl and observation of (18)O induced (13)C shifts in the pyran acetal product. NMR data of the synthetic C16-C28 fragment compared favorably to the natural product providing support of the assigned stereochemistry.     

Synthesis of novel 15-membered macrolide derivatives

In order to develop new antibiotics effective against resistant bacteria,a series of novel 15-membered macrolide derivatives were designed and synthesized by the modification of hydroxyl groups at C-11,C-12 and C-4＂ positions.Their structures were confirmed by MS,IR,^1H NMR or ^13C NMR.