A total synthesis of millingtonine A

A total synthesis of millingtonine A, a diglycosylated alkaloid, has been accomplished. Millingtonine A possesses a unique racemic tricyclic core structure not known from any other natural or synthetic source until now. The synthesis features a key bond-forming radical Ueno-Stork cyclization to form the heterocyclic core.     

Bioinspired Total Synthesis of Complex Nucleoside Antibiotics A201A,A201D and A201E

Herein, bioinspired total syntheses of A201A, A201D, and A201E based on a previously reported biosynthetic pathway are presented. The challenging 1,2-cis-furanoside, a core structure of the A201 family, was obtained by remote 2-quinolinecarbonyl-assisted glycosylation. We accomplished the total synthesis of A201A and A201E based on the critical 1,2-cis-furanoside moiety through late-stage glycosylation without any interference from basic dimethyl adenosine. We also confirmed the absolute configuration of A201E by total synthesis. This modular synthesis strategy enables efficient preparation of A201 family antibiotics, allowing the study of their structure–activity relationships and mode of action. This study satisfies the increasing demand for developing novel antibiotics inspired by the A201 family.     

Bioinspired Total Synthesis of Complex Nucleoside Antibiotics A201A,A201D and A201E

Herein, bioinspired total syntheses of A201A, A201D, and A201E based on a previously reported biosynthetic pathway are presented. The challenging 1,2-cis-furanoside, a core structure of the A201 family, was obtained by remote 2-quinolinecarbonyl-assisted glycosylation. We accomplished the total synthesis of A201A and A201E based on the critical 1,2-cis-furanoside moiety through late-stage glycosylation without any interference from basic dimethyl adenosine. We also confirmed the absolute configuration of A201E by total synthesis. This modular synthesis strategy enables efficient preparation of A201 family antibiotics, allowing the study of their structure–activity relationships and mode of action. This study satisfies the increasing demand for developing novel antibiotics inspired by the A201 family.     

A total synthesis of mycalisine A

In this paper, we report a total synthesis of a naturally occurring pyrrolo[2,3-d]pyrimidine nucleoside, mycalisine A. Our synthetic strategy uses D-xylose as the startingmaterial and Vorbrüggen glycosylation as the key step. Mycalisine A was synthesized in 11 steps with a 15% overall yield.     

A simple stereocontrolled synthesis of salinosporamide A

A simple and effective stereocontrolled synthesis of salinosporamide A has been developed. This process, the first synthesis of salinosporamide A, is capable of providing the compound in substantial quantities for further biological studies. Salinosporamide A was of special interest as a synthetic target because of its potent in vitro cytotoxic activity against many tumor cell lines (IC(50) values of 10 nM or less).     

Enantioselective syntheses of tremulenediol A and tremulenolide A

A concise entry to the skeleton of the tremulane sesquiterpenes is described that culminated in the first enantioselective syntheses of tremulenediol A and tremulenolide A. The approach features a series of efficient transition metal-catalyzed reactions commencing with an enantioselective rhodium(II)-catalyzed intramolecular cyclopropanation followed by a regioselective allylic alkylation and a diastereoselective rhodium(I)-catalyzed [5+2] cycloaddition.     

A concise total synthesis of salinosporamide A

A concise and straightforward 14-step total synthesis of (+/-)-salinosporamide A, based on a diastereoselective acid-catalysed intramolecular cyclisation of to the pyrrolidinone , and a regioselective reduction of the malonate derivative 8b to the aldehyde 9, is described.     

A total synthesis of phomactin A

A total synthesis of phomactin A (1) based on a Cr(II)/Ni(II) macrocyclisation from the aldehyde vinyl iodide 11, leading to 12, followed by elaboration of the epoxyketone 16, which then undergoes spontaneous pyran-hemiacetal formation on deprotection, is described.     

Separation of gibberellin A4 from A4 and A7 mixture by selective complex

<正>Gibberellin A4 is effectively separated from mixture of gibberellin A4 and its analogue gibberellin A7,in the form of its crystalline complex with N,N,N',N'-tetramethylethylenediamine.After removing the tetramethylethylenediamine from the crystal by dilute HCl,gibberellin A4 is obtained a purity of 98.1%and a yield of 72.7%.     

Pre-resonance Raman studies of some mesogens-TB4A, TB7A and TB10A

Pre-resonance Raman spectra of certain liquid crystalline compounds, TB4A, TB7A and TB10A, are reported. The anomaly observed in the pre-resonance Raman spectra in the three compounds was initially explained by the Albrecht-Hutley Model, but its failure leads us to explain the anomalous intensity enhancement mechanism by invoking an interference effect between a weak dipole-forbidden excited state and a nearby strong electronic level via vibrational modes. The presence of a 2¹A_g dipole-forbidden excited state in TB4A and TB10A is deduced after an elaborate discussion of their centro-symmetric structure. The structural difference of TB7A in comparison with TB4A and TB10A is also discussed by taking their X-ray data into consideration.     

Pre-resonance Raman studies of some mesogens-TB4A,TB7A and TB10A

Pre-resonance Raman spectra of certain liquid crystalline compounds, TB4A, TB7A and TB10A, are reported. The anomaly observed in the pre-resonance Raman spectra in the three compounds was initially explained by the Albrecht-Hutley Model, but its failure leads us to explain the anomalous intensity enhancement mechanism by invoking an interference effect between a weak dipole-forbidden excited state and a nearby strong electronic level via vibrational modes. The presence of a 2¹A_g dipole-forbidden excited state in TB4A and TB10A is deduced after an elaborate discussion of their centro-symmetric structure. The structural difference of TB7A in comparison with TB4A and TB10A is also discussed by taking their X-ray data into consideration.     

Synthesis of the tricyclic core of labiatin A and australin A

A concise synthesis of the tricyclic core of the marine diterpene natural products labiatin A and australin A has been accomplished. The key ring-forming transformation is a cascade reaction comprising generation of a copper carbenoid from a diazo ketone, intramolecular reaction of the carbenoid with a cyclic ether, and rearrangement of the resulting free oxonium ylide or its metal-bound equivalent with ring expansion of the original cyclic ether.     

Total synthesis of mycalamide A and 7-epi-mycalamide A

[formula: see text] The final stages of a total synthesis of mycalamide A are described. A key step is the aldol reaction (mismatched) of imide 4 and aldehyde 5 which provided a ca. 5:4 mixture of aldols 10a and 10b, with incorrect C(7) stereochemistry. Elaboration of the 10a-10b mixture to mycalamide A required epimerization of C(7) at the stage of beta-keto imide 11. Alternatively, Swern oxidation of the 10a-10b mixture under conditions that minimize C(7) epimerization led to 7-epi-mycalamide A selectively.     

A symmetry-based formal synthesis of zaragozic acid A

A symmetry-based strategy for the synthesis of the zaragozic acids is reported. Two enantioselective dihydroxylations were used to establish the absolute configuration of a C(2) symmetric intermediate. Noteworthy transformations include a group-selective lactonization, which accomplished an end-differentiation of a pseudo-C(2) symmetric intermediate. Late stage protecting group adjustments and oxidations accomplished a formal synthesis of zaragozic acid A.     

Asymmetric Synthesis of the Ring A Substructure of Genkwadane A

A practical approach to the asymmetric synthesis of the ring A substructure of genkwadane A, a daphnane diterpenoid, was developed. This synthesis features the Mukaiyama aldol reaction to introduce the quaternary stereogenic center at C4 and VO(acac)₂‐catalyzed Jackson‐Ellman‐Bolm sulfoxidation to deliver the corresponding sulfoxide. The Dieckmann‐type condensation was efficiently promoted by KHMDS and the ring A substructure was finally accomplished through Barton iodination condition.     

Enantioselective syntheses of tremulenediol A and tremulenolide A

[reaction: see text] An enantioselective entry to the skeleton of the tremulane sesquiterpenes is described. The approach features a series of efficient transition metal-catalyzed reactions commencing with an enantioselective rhodium(II)-catalyzed intramolecular cyclopropanation followed by a regioselective allylic alkylation and a diastereoselective rhodium(I)-catalyzed [5 + 2] cycloaddition. This strategy was applied to the first enantioselective syntheses of tremulenediol A and tremulenolide A.     

A brief synthesis of (-)-englerin A

Englerins A and B are guaiane sesquiterpenes that were isolated from the bark of Phyllanthus engleri, a plant indigenous to east Africa. The englerins consist of a 5-6-5 fused tricyclic structure with an ether bridge and two ester-bearing stereogenic centers, including a highly unusual glycolate residue. Englerin A is a potent and selective inhibitor of the growth of six human renal cancer cell lines. We report herein an efficient, eight-step synthesis of englerin A that leverages simple carbonyl-enabled carbon-carbon bond formations. Our route is amenable to the production of a diverse series of analogues for structure-function studies and determination of the mode of action of these natural products.     

A short enantioselective synthesis of a component of cryptophycin A and arenastatin A

Synthesis of 1, a component of cryptophycin A 2 and arenastatin A 3, was achieved by applying palladium-catalyzed reductive ring opening of optically active alkenyl oxirane 13 for the construction of the vicinal stereogenic centers.     

Influence of selectivity on the supramolecular polymerization of AB-type polymers capable of Both A x A and A x B interactions

The supramolecular polymerization of two AB-type monomers capable of hydrogen-bond-mediated A x B heterocoupling and A x A homocoupling is discussed. The AB-type supramolecular polymerization is based on the strong interaction between self-dimerizing 2-ureido-pyrimidinone (UPy) and 2,7-diamido-1,8-naphthyridine (NaPy). In an effort to reduce the "self-stoppered" effect that is inherently present in these supramolecular polymerizations we used a novel ureido-pyrimidinone substituted with a dibutylamino group at the pyrimidinone ring. As a result of the substitution, the dimerization constant of the novel UPy unit is lowered compared to the previous UPy unit while the heterodimerization strength is retained. Unexpectedly, the increased selectivity toward heteroassociation not only influences the concentration-dependent degree of polymerization due to reduction of the "self-stoppered" effect but also has a pronounced effect on the ring-chain equilibrium by increasing the tendency to cyclize. In order to quantitatively explain our results, a model was developed that accurately predicts the degree of polymerization by taking into account homo- and heterodimerization as well as cyclization. Finally, molecular weight distributions for noncyclizing AB supramolecular polymerizations with and without a reversible A x A interaction are calculated. It is found that the molecular weight distribution becomes narrower when A x A interactions are present.     

A modified total synthesis of cystothiazole A

A modified total synthesis of cystothiazole A is described. In this synthetic strategy, a one-step transformation of acylated oxazolidinone to β-ketoester has been successfully applied, thus making the synthetic route more efficient. This method may also be potentially applied in synthesis of other related β-substituted-β-methoxyl acrylates (bb-MOAs).