A mild and selective deprotection of p-methoxybenzyl (PMB) ether by magnesium bromide diethyl etherate-methyl sulfide

1,4-Dimethoxynaphthalene-2-methyl ('DIMON'), an oxidatively labile protecting group for synthesis of polyunsaturated lipids

A new benzyl-type protecting group (1,4-dimethoxynaphthalene-2-methyl, 'DIMON') for hydroxyl functions can be selectively removed under oxidative conditions without damaging polyunsaturated fatty acyl groups. Its application is shown by the first synthesis of an ether (plasmanyl) phospholipid containing the docosa-(4Z,7Z,10Z,13Z,16Z,19Z)-hexaenoyl group.

Synthesis and Bioactivity of Ophiofuranones A and B

Ophiofuranones A and B, metabolites of the fungus Ophiosphaerella korrae, were synthesized in 16 steps and 12%/22% yield. The stereogenic centers were established by Sharpless dihydroxylations and epoxidation, the 1,3-dienes via Wittig or HWE olefinations. The rings were closed through Knoevenagel-type condensation and lactonization. The ophiofuranones proved nontoxic at relevant concentrations against tumor cells, fibroblasts, and various bacteria and fungi. Ophiofuranone A and the monocyclic precursors 4 were weakly active against microbial biofilms.

A Facile, Efficient and Selective Deprotection of P - Methoxy Benzyl Ethers Using Zinc (II) Trifluoromethanesulfonate

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Deprotection is significant and conducted over mild reaction conditions, in order to restrict any more side reactions with sensitive functional groups as well as racemization or epimerization of stereo center because the protective groups are often cleaved at last stage in the synthesis. P - Methoxy benzyl (PMB) ether appears unique due to its easy introduction and removal than the other benzyl ether protecting groups. A facile, efficient and highly selective cleavage of P - methoxy benzyl ethers was reported by using 20 mole% Zinc (II) Trifluoromethanesulfonate at room temperature in acetonitrile solvent over 15-120 min. time period. To study the generality of this methodology, several PMB ethers were prepared from a variety of substrates having different protecting groups and subjected to deprotection of PMB ethers using Zn(OTf)2 in acetonitrile. In this methodology, zinc triflate cleaves only PMB ethers without affecting acid sensitivity, base sensitivity and also chiral epoxide groups.

Stereoselective construction of 2-vinyl 3-hydroxybenzopyran rings: total syntheses of teadenols A and B

Total syntheses of teadenols A and B, isolated from fermented tea, were accomplished in a highly stereocontrolled manner.

Total synthesis of (+)-trienomycins A and F via C-C bond-forming hydrogenation and transfer hydrogenation

The triene-containing C17-benzene ansamycins trienomycins A and F were prepared in 16 steps (longest linear sequence, LLS) and 28 total steps. The C11-C13 stereotriad was generated via enantioselective Ru-catalyzed alcohol CH syn crotylation followed by chelation-controlled carbonyl dienylation. Enantioselective Rh-catalyzed acetylene-aldehyde reductive coupling mediated by gaseous H2 was used to form a diene that ultimately was subjected to diene-diene ring closing metathesis to form the macrocycle. The present approach is 14 steps shorter (LLS) than the prior syntheses of trienomycins A and F, and 8 steps shorter than any prior synthesis of a triene-containing C17-benzene ansamycin.

Synthesis of the aminocyclitol units of (-)-hygromycin A and methoxyhygromycin from myo-inositol

Concise and efficient syntheses of the aminocyclitol cores of hygromycin A (HMA) and methoxyhygromycin (MHM) have been achieved starting from readily available myo-inositol. Reductive cleavage of myo-inositol orthoformate to the corresponding 1,3-acetal, stereospecific introduction of the amino group via the azide, and resolution of a racemic cyclitol derivative as its diastereomeric mandelate esters are the key steps in the synthesis. Synthesis of the aminocyclitol core of hygromycin A involved chromatography in half of the total number of steps, and the aminocyclitol core of methoxyhygromycin involved only one chromatography.

Synthesis and assessment of globotriose-chitosan conjugate, a novel inhibitor of shiga toxins produced by Escherichia coli

Shiga toxin (Stx)-producing Escherichia coli (STEC) causes diarrhea and colitis in humans that can develop into a life-threatening hemolytic uremic syndrome (HUS). Developing efficient means of controlling STEC diseases, for which no drugs or vaccines are currently available, remains a high priority. We report here the construction and development of chitosan conjugates bearing the Stx ligand trisaccharide globotriose to demonstrate their potential as STEC disease treatment agents. The synthesis was accomplished by grafting a globotriose derivative containing an aldehyde-functionalized aglycone to chitosan amino groups. The obtained globotriose-chitosan conjugate bound with high affinity to Stx and efficiently neutralized its toxicity on Vero cells. Moreover, Stx levels in the gut of infected mice receiving oral doses of the conjugate were greatly diminished, enabling the mice to resist a fatal STEC challenge. The conjugate appears to function as a Stx adsorbent in the gut, preventing toxin entry into the bloodstream and consequent development of HUS. As such, the conjugate could act as a novel agent against STEC disease.

Cyclic 1,2-diketones as core building blocks: a strategy for the total synthesis of (-)-terpestacin

We report a full account of our work towards the total synthesis of (-)-terpestacin (1), a sesterterpene originally isolated from fungal strain Arthrinium sp. FA1744. Its promising anti-HIV and anti-cancer activity, as well as its novel structure, make terpestacin an attractive synthetic target. A strategy based on the unique reactivity of cyclic 1,2-diketones (diosphenols) was developed and total synthesis of 1 was achieved in 20 steps, in the longest linear sequence, from commercially available 2-hydroxy-3-methyl-2-cyclopenten-1-one. The key feature of our synthesis is the double usage of a "Pd AAA-Claisen" protocol (AAA=asymmetric allylic alkylation), first in the early stages to generate the C1 quaternary center and then in the late stages to install the side chain. In addition, a rather unusual ene-1,2-dione moiety was synthesized and utilized as an excellent Michael acceptor to attach the C15 substituent. Several possible routes towards the total synthesis have been examined and carefully evaluated. During our exploration many interesting chemoselectivity issues have been addressed, such as a highly selective ring-closing metathesis and a challenging oxidation of a disubstituted olefin in the presence of three trisubstituted ones.

Synthesis of a 35-member stereoisomer library of bistramide A: evaluation of effects on actin state, cell cycle and tumor cell growth

Synthesis and preliminary biological evaluation of a 35-member library of bistramide A stereoisomers are reported. All eight stereoisomers of the C1-C13 tetrahydropyran fragment of the molecule were prepared utilizing crotylsilane reagents 9 and 10 in our [4+2]-annulation methodology. In addition, the four isomers of the C14-C18 gamma-amino acid unit were accessed via a Lewis acid mediated crotylation reaction with use of both enantiomers of organosilane 11. The spiroketal subunit of bistramide A was modified at the C39-alcohol to give another point of stereochemical diversification. The fragments were coupled by using a standard peptide coupling protocol to provide 35 stereoisomers of the natural product. These stereochemical analogues were screened for their effects on cellular actin and cytotoxicity against cancer cell lines (UO-31 renal and SF-295 CNS). The results of these assays identified one analogue, 1.21, with enhanced potency relative to the natural product, bistramide A.

Concise Asymmetric Total Synthesis of Scyphostatin, a Potent Inhibitor of Neutral Sphingomyelinase

The concise asymmetric total synthesis of scyphostatin has been achieved by condensation of the optically active cyclohexane unit, prepared from the commercially available 1,4-cyclohexadiene by our own method, and the side chain, prepared by the method developed by Hoye and Tennakoon (T. R. Hoye, M. A. Tennakoon, Org. Lett. 2000, 2, 1481-1483). The modification of the epoxy cyclohexenone unit was achieved in a late stage of the total synthesis, and deprotection of the primary alcohol was conducted in the final step. During the synthesis several key reactions were attained: 1) intramolecular bromoetherification of the cyclohexadiene acetal; 2) stereoselective introduction of the tertiary alcohol, 3) deprotection of the acetal function to the aldehyde by combination with silyl triflate/2,4,6-collidine and the one-pot synthesis of the disilyl aldehyde compounds, with different types of silyl groups, from the dihydroxy acetal compounds; and 4) facile deprotection of the 2,4-dimethoxyphenylmethyl ((2,4)DMPM) protecting group of the primary alcohol.

Discovery and preliminary SAR studies of a novel, nonsteroidal progesterone receptor antagonist pharmacophore

A series of 6-aryl-1,2-dihydro-2,2,4-trimethylquinolines was synthesized and tested for functional activity on the human progesterone receptor isoform B (hPR-B) in mammalian (CV-1) cells. The lead compound LG001447 (1,2-dihydro-2,2, 4-trimethyl-6-phenylquinoline) was discovered via directed high throughput screening of a defined chemical library utilizing an hPR-B cotransfection assay. Electron-withdrawing substituents at the meta position of the C(6) aryl group afforded substantial improvements in hPR modulatory activity. Several analogues were able to potently block the effects of progesterone in vitro. Two compounds, 10 (LG120753) and 11 (LG120830) with potencies comparable or equal to the steroidal hPR antagonist onapristone (ZK98,299), were demonstrated to act as antiprogestins in vivo after oral administration to rodents. This is the first disclosure of orally active nonsteroidal antiprogestins.

Preparation, resolution, and biological evaluation of 5-aryl-1, 2-dihydro-5H-chromeno[3,4-f]quinolines: potent, orally active, nonsteroidal progesterone receptor agonists

Two potent nonsteroidal progestins from the 5-aryl-1, 2-dihydro-5H-chromeno[3,4-f]quinoline class (LG120746 and LG120747) were selected for scale-up, resolution, and biological evaluation of the purified enantiomers. For each quinoline, the levorotatory enantiomer was determined to be the more potent agonist of the human progesterone receptor isoform B (hPR-B) (EC50 < 3 nM), but the dextrorotatory enantiomers retained significant PR modulatory activity (EC50 < 200 nM). In two in vivo rodent models of progestational activity, a pregnancy maintenance assay and a uterine wet weight assay, the two eutomers displayed potent progesterone-like effects. In a third model for progestational activity, the mammary end bud assay, these compounds were significantly less active. These studies demonstrate that certain members of this class of selective progesterone receptor modulators display encouraging and potentially useful tissue-selective progestational effects.