Total synthesis of ionophore antibiotic X-14547A

CuBr2-catalyzed diastereoselective allylation: total synthesis of decytospolides A and B and their C6-epimers

An efficient CuBr₂-catalyzed diastereoselective allylation of a cyclic hemiacetal with allyltrimethylsilane as a nucleophile has been developed. The protocol offers a cost effective, protecting group tolerant, and operationally simple approach to 2,6-trans-disubstituted tetrahydropyran with excellent diastereoselectivity. Furthermore, the application of this methodology has been demonstrated in the total synthesis of decytospolides A and B and their C6-epimers.

Using batch reactor results to calculate optimal flow rates for the scale-up of UV photochemical reactions

A simple method for the accurate calculation of optimal flow rates for photochemical reactions from optimized batch results is described and demonstrated in the scale-up of three challenging examples.

From symmetric glycerol derivatives to dissymmetric chlorohydrins

The anticipated worldwide increase in biodiesel production will result in an accumulation of glycerol for which there are insufficient conventional uses. The surplus of this by-product has increased rapidly during the last decade, prompting a search for new glycerol applications. We describe here the synthesis of dissymmetric chlorohydrin esters from symmetric 1,3-dichloro-2-propyl esters obtained from glycerol. We studied the influence of two solvents: 1,4-dioxane and 1-butanol and two bases: sodium carbonate and 1-butylimidazole, on the synthesis of dissymmetric chlorohydrin esters. In addition, we studied the influence of other bases (potassium and lithium carbonates) in the reaction using 1,4-dioxane as the solvent. The highest yield was obtained using 1,4-dioxane and sodium carbonate.

Synthesis of 2beta-substituted-14-epi-previtamin D3 and testing of its genomic activity

2beta-substituted analogs of 14-epi-previtamin D(3) were synthesized for the first time by the thermal isomerization of the corresponding 14-epi-vitamin D3 that were available using coupling reaction between the A-ring phosphine oxide derived from a chiral epoxide and CD-ring cis-hydrindanone. The VDR binding affinity and transactivation activity of osteocalcin promoter in HOS cells were evaluated, and the new analogs were found to be less active, 0.01-0.18% of VDR binding affinity compared with the natural hormone and EC50 1.0-9.1 nM for transactivation activity, than 14-epi-previtamin D3 with 0.5% (VDR) and EC50 0.46 nM, respectively.

Synthesis and preliminary biological evaluation of 20-epi-eldecalcitol [20-epi-1alpha,25-dihydroxy-2beta-(3-hydroxypropoxy)vitamin D3: 20-epi-ED-71]

Eldecalcitol [1alpha,25-dihydroxy-2beta-(3-hydroxypropoxy)vitamin D3, developing code: ED-71] is an analog of active vitamin D3, 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3] that possesses a hydroxypropoxy substituent at the 2beta-position of 1,25(OH)2D3. Eldecalcitol has potent biological effects on bone and is now in preparation for approval as a promising medicine for the treatment of osteoporosis in Japan. To explore chemical structure-biological activity relationships between eldecalcitol and related analogs, we have already synthesized 1-epi-eldecalcitol, 3-epi-eldecalcitol, and 1,3-diepi-eldecalcitol with inherent biological interests of each targeted analog and evaluated their biological responses. It has been reported that 20-epi-1,25(OH)2D3, a diastereomer of 1,25(OH)2D3 that possesses an inverted methyl substituent at the 20-position of the side chain, shows remarkably enhanced biological activities compared to parental compound, 1,25(OH)2D3. As a continuation of our modification studies on eldecalcitol, we took great interest in 20-epi-eldecalcitol and its biological responses. In this paper, the synthesis of 20-epi-eldecalcitol by the Trost coupling reaction between the A-ring fragment and the C/D-ring fragment as well as in vitro preliminary biological evaluation of 20-epi-eldecalcitol are described. In the induction of human myeloid leukemia cell (HL-60) differentiation, inhibition of the human histiocytic lymphoma cell (U937) proliferation, and increase in osteocalcin concentration in the human osteosarcoma cell (MG-63), 20-epi-eldecalcitol showed significantly enhanced activity compared to eldecalcitol.

Efficient synthesis of the C(7)-C(20) subunit of amphidinolides C and F

Synthesis of the C(7)-C(20) subunit of amphidinolides C and F has been accomplished utilizing a Me(3)Al-mediated ring opening of a vinyl iodide/allylic epoxide to establish the C(12,13)anti stereochemistry, an organolithium coupling/olefination sequence to construct the C(9)-C(11) diene moiety and a sulfone alkylation/hydroxylation strategy to join the C(7)-C(14) and C(15)-C(20) fragments.

The Diels--Alder reaction in total synthesis

The Diels-Alder reaction has both enabled and shaped the art and science of total synthesis over the last few decades to an extent which, arguably, has yet to be eclipsed by any other transformation in the current synthetic repertoire. With myriad applications of this magnificent pericyclic reaction, often as a crucial element in elegant and programmed cascade sequences facilitating complex molecule construction, the Diels-Alder cycloaddition has afforded numerous and unparalleled solutions to a diverse range of synthetic puzzles provided by nature in the form of natural products. In celebration of the 100th anniversary of Alder's birth, selected examples of the awesome power of the reaction he helped to discover are discussed in this review in the context of total synthesis to illustrate its overall versatility and underscore its vast potential which has yet to be fully realized.

Reduction of pyrrolyl- and indolylamides with BH3 x THF: cyclodeoxygenation versus deoxygenation

Herein we report that borane reductions of acylpyrroles and acylindoles that contain a pendant phenol take two different paths. Acylpyrroles undergo a reductive cyclization to make unusual chromanyl pyrroles. Treatment of related acylindoles under identical conditions results in deoxygenation without cyclization. The results are interpreted in terms of relative rates of cyclization and reduction of intermediate carbenium ions, where cyclization of the indole-stabilized carbenium ion is slower.

Total synthesis studies on macrocyclic pipecolic acid natural products: FK506, the antascomicins and rapamycin

This chapter derives its inspiration from the challenges presented to total synthesis chemists, by a particular group of macrocyclic pipecolic acid natural products. Although there is considerable emphasis on the completed syntheses of the main characters (FK506 (1), the antascomycins (4 and 5) and rapamycin (7)), the overall complexity of the molecular problem has stimulated a wealth of new knowledge, including the development of novel strategies and the invention of new synthetic methods. The ingenious and innovative approaches to these targets have enabled new generations of analogues, and provided material to further probe the biology of these fascinating molecules. With pharmaceutical application as an immunosuppressant, as well as potential use for the treatment of cancer and neurodegenerative diseases, this family of natural products continues to inspire new and interesting science while providing solutions to healthcare problems of the world.

Synthetic Approach Toward the Total Synthesis of Kempane Diterpenes via Transannular Diels−Alder Strategy

Total syntheses of two new (+/-)-kempane derivatives 30 and 47 were achieved with transannular Diels-Alder reaction (TADA) serving as the key step for the stereoselective formation of tricyclic [6.6.5] system 3. This synthetic approach also reveals that the geometry of the C3 group of such a tricyclic system plays an important role for the formation of the seven-membered kempane skeleton.

Enzyme-Mediated Preparation of the Enantiomerically Enriched Isomers of the Odorous Tetrahydropyranyl AcetatesJasmal® andJessemal®, and Their Olfactory Evaluation

All four stereoisomers of the fragrance Jasmal of structure 3,4,5,6-tetrahydro-3-pentyl-2H-pyran-4-yl acetate were prepared by enzymatic resolutions of the corresponding alcohols. The absolute configurations were unambiguously determined by comparison with the enantiomer (3R,4S)-1 prepared from L-tartaric acid. The four stereoisomers of the fragrance Jessemal of structure 3-butyl-5-methyl-3,4,5,6-tetrahydro-2H-pyran-4-yl acetate were obtained starting from the epoxy alcohol 10, which was obtained in an optically pure state by enzymatic resolution of the racemic mixture. The olfactory evaluations of all stereoisomers are reported. (1)H-NMR Conformational analysis of diastereoisomers (3RS,4RS,5RS)-2 and (3RS,4SR,5RS)-2 is also reported.

Discovery of Novel Phenolic Antioxidants as Inhibitors of Vascular Cell Adhesion Molecule-1 Expression for Use in Chronic Inflammatory Diseases

Vascular cell adhesion molecule-1 (VCAM-1) mediates recruitment of leukocytes to endothelial cells and is implicated in many inflammatory conditions. Since part of the signal transduction pathway that regulates the activation of VCAM-1 expression is redox-sensitive, compounds with antioxidant properties may have inhibitory effects on VCAM-1 expression. Novel phenolic compounds have been designed and synthesized starting from probucol (1). Many of these compounds demonstrated potent inhibitory effects on cytokine-induced VCAM-1 expression and displayed potent antioxidant effects in vitro. Some of these derivatives (4o, 4p, 4w, and 4x) inhibited lipopolysaccharide (LPS)-induced secretion of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and IL-6 from human peripheral blood mononuclear cells (hPBMCs) in a concentration-dependent manner in vitro and showed antiinflammatory effects in an animal model. Compounds 4ad and 4ae are currently in clinical trials for the treatment of rheumatoid arthritis (RA) and prevention of chronic organ transplant rejection, respectively.

Silver(I) oxide mediated highly selective monotosylation of symmetrical diols. Application to the synthesis of polysubstituted cyclic ethers

[reaction: see text] The reaction of symmetrical diols and oligo(ethylene glycol)s with a stoichiometric amount of p-toluenesulfonyl chloride in the presence of silver(I) oxide and a catalytic amount of potassium iodide led selectively to the monotosylate derivatives in high yields. Polysubstituted cyclic ethers were obtained readily upon treatment of the corresponding diols with an excess of silver oxide. The high selectivity was explained on the basis of the difference in acidity between the two hydroxy groups, which undergo an intramolecular hydrogen bonding.

Synthesis and biological characterization of 1alpha,24,25-trihydroxy-2beta-(3-hydroxypropoxy)vitamin D(3) (24-hydroxylated ED-71)

24-Hydroxylated derivatives were synthesized in 24(R) and 24(S) forms by the convergent method as analogs related to 1alpha,25-dihydroxy-2beta-(3-hydroxypropoxy)vitamin D(3). In the convergent synthesis, the A-ring fragment, synthesized from diethyl D-tartarate, and the C/D-ring fragments in 24(R) and 24(S) forms (vitamin D numbering), obtained from vitamin D(2) via the Inhoffen-Lythgoe diol, were coupled in moderate yields to give 1alpha,24(R),25-trihydroxy-2beta-(3-hydroxypropoxy)vitamin D(3) and 1alpha,24(S),25-trihydroxy-2beta-(3-hydroxypropoxy)vitamin D(3). In preliminary biological evaluations, 24-hydroxylation of 1alpha,25-dihydroxy-2beta-(3-hydroxypropoxy)vitamin D(3) caused weakened affinity to vitamin D binding protein in vitro and less calcemic activity in vivo compared to the parent compound. While the affinity to vitamin D receptor in 24(R) epimer was sustained, the affinity in 24(S) epimer was less than that of the parent compound.

Synthesis of cryptophycin 52 using the sharpless asymmetric dihydroxylation: diol to epoxide transformation optimized for a base-sensitive substrate

A synthesis of cryptophycin 52 (2) is reported using a Sharpless asymmetric dihydroxylation (AD) strategy to install the epoxide moiety. The high stereoselectivity of the AD reaction that allows for an efficient means of preparing the epoxide is in contrast to the standard direct epoxidation of cryptophycin substrates, which proceeds with poor diastereoselectivity. Methodology for conversion of the diol AD product to the requisite epoxide is disclosed. The transformation has been optimized to proceed in high yield in the presence of base sensitive functionality.