Synthesis of a C1-C21 subunit of the protein phosphatase inhibitor tautomycin: a formal total synthesis

Zn-Catalyzed enantioselective allylation and allenylation of isatins by virtue of a proline-derived chiral ligand

An asymmetric allylation and allenylation of isatins with facile organoboron reagents was developed under the catalysis of a Lewis acid. A series of optically pure 3-allyl-3-hydroxyoxindoles and 3-allenyl-3-hydroxyoxindoles can be obtained in excellent yields (up to 99% yield) and high enantioselectivities (up to 97% ee). The possible transition state was supported by DFT calculation and the corresponding mechanism was proposed. A gram scale experiment and further functionalization of these chiral 3-hydroxyoxindoles are established.

First synthesis of (S)-(+)-hymenoic acid, a DNA polymerase λ inhibitor isolated from Hymenochaetaceae sp

Hymenoic acid, isolated from cultures of the fungus, Hymenochaetaceae sp., is a specific inhibitor of DNA polymerase λ. The first synthesis of (S)-(+)-hymenoic acid was achieved by starting from trans-1,4-cyclohexanedimethanol and methyl (R)-(−)-3-hydroxyisobutyrate, and Julia–Kocienski olefination was employed as the key step.

Total synthesis of (+)-18-epi-latrunculol A: development of a synthetic route

The evolution of an enantioselective total synthesis of (+)-18-epi-latrunculol A, a congener of the marine-sponge-derived latrunculins A and B, is reported. Key steps include a late-stage Mitsunobu macrolactonization to construct the 16-membered macrolactone, a mild Carreira alkynylation to unite the northern and southern hemispheres, a diastereoselective, acid-mediated δ-hydroxy enone cyclization/equilibration sequence, and a functional-group-tolerant cross-metathesis to access the enone cyclization precursor.

Total synthesis of (+)-18-epi-latrunculol A

An enantioselective total synthesis of the cytotoxic latrunculin congener (+)-18-epi-latrunculol A has been achieved. Key steps in the synthetic route include an acid-mediated enone cyclization/equilibration sequence, a Carreira alkynylation, and a late-stage Mitsunobu macrolactonization to construct the macrolide skeleton.

A piperidine chiron for the Veratrum alkaloids

A Veratrum piperidine chiron was prepared over 11 steps (7.9% yield) from (-)-citronellal. Three methods for the installation of the propargylic side chain onto a cyclic enamide are presented.

Zinc-catalyzed allenylations of aldehydes and ketones

The general zinc-catalyzed allenylation of aldehydes and ketones with an allenyl boronate is presented. Preliminary mechanistic studies support a kinetically controlled process wherein, after a site-selective B/Zn exchange to generate a propargyl zinc intermediate, the addition to the electrophile effectively competes with propargyl-allenyl zinc equilibration. The utility of the methodology was demonstrated by application to a rhodium-catalyzed [4+2] cycloaddition.

Highly enantioselective reduction of 4-(trimethylsilyl)-3-butyn-2-one to enantiopure (R)-4-(trimethylsilyl)-3-butyn-2-ol using a novel strain Acetobacter sp. CCTCC M209061

The biocatalytic reduction of 4-(trimethylsilyl)-3-butyn-2-one to enantiopure (R)-4-(trimethylsilyl)-3-butyn-2-ol was successfully conducted with high enantioselectivity using immobilized whole cells of a novel strain Acetobacter sp. CCTCC M209061, newly isolated from kefir. Compared with other microorganisms that were investigated, Acetobacter sp. CCTCC M209061 was shown to be more effective for the bioreduction reaction, and afforded much higher yield and product enantiomeric excess (e.e.). The optimal buffer pH, co-substrate concentration, reaction temperature, substrate concentration and shaking rate were 5.0, 130.6 mM, 30 degrees C, 6.0 mM and 180 r/min, respectively. Under the optimized conditions, the maximum yield and the product e.e. were 71% and >99%, respectively, which are much higher than those reported previously. Additionally, the established biocatalytic system proved to be efficient for the bioreduction of acetyltrimethylsilane to (R)-1-trimethylsilylethanol with excellent yield and product e.e. The immobilized cells manifested a good operational stability under the above reaction conditions since they retained 70% of their catalytic activity after ten cycles of use.

Taste acuity in response to zinc supplementation in older Europeans

Taste acuity declines with age and may be dependent upon Zn status. The aim of the present double-blind, randomised controlled intervention trial has been to determine taste acuity in response to Zn supplementation (placebo, or 15 or 30 mg Zn/d). Healthy older European adults aged 70–87 years were recruited within Italy (Rome) (n 108) and France (Grenoble) (n 91) to the European Commission-funded Zenith project. A signal detection theory approach was adopted for taste assessment. The data were converted to R indices and analysed by repeated-measures ANOVA controlling for baseline taste acuity as well as serum and erythrocyte Zn. Serum Zn increased post-intervention, indicating compliance with the intervention. Results differed across geographical region. Salt taste acuity was greater in response to Zn (30 mg) than placebo post-intervention among those recruited in Grenoble. There was no apparent change in acuity for sweet, sour or bitter taste in response to Zn. Supplemented Zn may have potential to enhance salt taste acuity in those over the age of 70 years. Further research is required to determine if enhanced salt taste acuity is reflected in the eating experiences of older individuals.

Total synthesis of halipeptins: isolation of halipeptin D and synthesis of oxazoline halipeptin analogues

The isolation from the marine sponge Leiosella cf. arenifibrosa and structural elucidation of halipeptin D (5), a relative of the previously isolated halipeptins A-C (1-3), is described along with the total synthesis of a number of oxazoline analogues (7 a-d and epi-7 c-d). The developed synthetic strategy provides a flexible entry into the various isomers of the polyketide domain of the halipeptins and improvises for a late stage construction of the oxazoline ring after a macrolactamization process which secures the required macrocycle.

(R)- and (S)-4-TIPS-3-butyn-2-ol. Useful Precursors of Chiral Allenylzinc and Indium Reagents

A convenient route to the enantiomers of 4-TIPS-3-butyn-2-ol of >95% enantiomeric purity by reduction of the ynone precursor 4 with the Noyori N-tosyl-1,2-diphenylethylenediamineruthenium cymene catalyst is described. The mesylate derivative of the (S) enantiomer (1c) is converted in situ to an allenylzinc or indium reagent in the presence of a catalyst derived from Pd(OAc)2 and Ph3P and either Et2Zn or InI. A second in situ addition of these reagents to aldehydes leads to anti homopropargylic alcohol adducts. The additions proceed in generally high (60-90%) yield with modest to excellent diastereoselectivity and high enantioselectivity. Only slight mismatching (<5%) is observed with chiral alpha-methyl and alpha-silyloxy aldehydes. Additions to alpha-substituted enals are highly diastereoselective, while beta,beta-disubstituted enals afford ca. 2:1 mixtures of anti and syn adducts.

Boron-Mediated Stereoselective Syntheses of γ,γ-Disubstituted Allenamides

Propargylic boranes generated by lithiation of optically active N-propargyloxazolidinones undergo reaction with a range of aldehydes to produce gamma,gamma-disubstituted allenamides with good diastereoselectivity.

Flexible Synthesis of Enantiomerically Pure 2,8-Dialkyl-1,7-dioxaspiro[5.5]undecanes and 2,7-Dialkyl-1,6-dioxaspiro[4.5]decanes from Propargylic and Homopropargylic Alcohols

A new approach to enantiomerically pure 2,8-dialkyl-1,7-dioxaspiro[5.5]undecanes and 2,7-dialkyl-1,6-dioxaspiro[4.5]decanes is described and utilizes enantiomerically pure homopropargylic alcohols obtained from lithium acetylide opening of enantiomerically pure epoxides, which are, in turn, acquired by hydrolytic kinetic resolution of the corresponding racemic epoxides. Alkyne carboxylation and conversion to the Weinreb amide may be followed by triple-bond manipulation prior to reaction with a second alkynyllithium derived from a homo- or propargylic alcohol. In this way, the two ring components of the spiroacetal are individually constructed, with deprotection and cyclization affording the spiroacetal. The procedure is illustrated by acquisition of (2S,5R,7S) and (2R,5R,7S)-2-n-butyl-7-methyl-1,6-dioxaspiro[4.5]-decanes (1), (2S,6R,8S)-2-methyl-8-n-pentyl-1,7-dioxaspiro[5.5]undecane (2), and (2S,6R,8S)-2-methyl-8-n-propyl-1,7-dioxaspiro[5.5]undecane (3). The widely distributed insect component, (2S,6R,8S)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane (4), was acquired by linking two identical alkyne precursors via ethyl formate. In addition, [(2)H(4)]-regioisomers, 10,10,11,11-[(2)H(4)] and 4,4,5,5-[(2)H(4)] of 3 and 4,4,5,5-[(2)H(4)]-4, were acquired by triple-bond deuteration, using deuterium gas and Wilkinson's catalyst. This alkyne-based approach is, in principle, applicable to more complex spiroacetal systems not only by use of more elaborate alkynes but also by triple-bond functionalization during the general sequence.

Syntheses and Reactions of Optically Active α-Aminoallenylstannanes

Lithiation/stannylation of optically active N-propargyloxazolidinones produced optically active alpha-oxazolidinonylallenylstannanes. Reaction of these with aldehydes in the presence of BF(3).OEt(2) produced beta-hydroxypropargylamines with high syn diastereoselectivity and ee. These were converted to gamma-hydroxy-beta-amino acids by oxidative cleavage of the alkyne.

Total synthesis of (-)-callystatin A

A total synthesis of the cytotoxic polyketide marine natural product callystatin A is described. The route features chiral allenylmetal additions to construct the polypropionate C15-22 segment and an sp(2)-sp(3) Suzuki coupling to join the C1-C11 and C12-C22 subunits.

Total synthesis of bafilomycin V(1): a methanolysis product of the macrolide bafilomycin C(2)

A synthesis of bafilomycin V(1), a methanolysis product of the macrolide natural product bafilomycin C(2), is described. The route utilizes chiral nonracemic allenylzinc reagents, prepared in situ from propargylic mesylates, to access key segments of this methyl ester. The acetylenic moieties of the derived homopropargylic alcohol adducts play an important role in further elaboration of these subunits. Final assemblage of the 25-carbon chain, containing 12 stereocenters, an alpha-methoxy Z,E 1,3-dienic ester, and an additional E,E 1,3-diene, was achieved through Stille coupling of an acetylene-derived vinyl stannane and vinyl iodide of approximate equal complexity. Attempted cyclization of several C15 hydroxy acid derivatives to the 16-membered lactone bafilomycin A(1), a potent inhibitor of vacuolar ATPases, could not be achieved.

Lipase-mediated resolution of 4-TMS-3-butyn-2-ol and use of the mesylate derivatives as a precursor to a highly stereoselective chiral allenylindium reagent

[reaction: see text]. An improved procedure for the resolution of 4-trimethylsilyl-3-butyn-2-ol has been developed. The mesylate derivatives of the resolved alcohols have been found to undergo highly enantio-, regio-, and diastereoselective additions to aldehydes, leading to homopropargylic alcohol adducts.