Asymmetric syntheses of the homalium alkaloids (-)-(s,s)-homaline and (-)-(r,r)-hopromine

The highly diastereoselective conjugate additions of the novel lithium amide reagents lithium (R)-N-(3-chloropropyl)-N-(α-methylbenzyl)amide and lithium (R)-N-(3-chloropropyl)-N-(α-methyl-p-methoxybenzyl)amide to α,β-unsaturated esters were used as the key steps in syntheses of the homalium alkaloids (-)-(S,S)-homaline and (-)-(R,R)-hopromine. The asymmetric synthesis of (-)-(S,S)-homaline was achieved in 8 steps and 18% overall yield, and the asymmetric synthesis of (-)-(R,R)-hopromine was achieved in 9 steps and 23% overall yield, from commercially available starting materials in each case. These syntheses therefore represent by far the most efficient total asymmetric syntheses of these alkaloids reported to date. A sample of the (4'R,4'S)-epimer of hopromine was also produced using this approach, which provided the first unambiguous confirmation of its absolute configuration and therefore that of natural (-)-(R,R)-hopromine.     

Asymmetric synthesis of (4R,5R)-cytoxazone and (4R,5S)-epi-cytoxazone

(4R,5R)-Cytoxazone has been prepared in four steps and in 61% overall yield and >98% ee. Conjugate addition of lithium (R)-N-benzyl-N-[small alpha]-methylbenzylamide to tert-butyl (E)-3-(p-methoxyphenyl)prop-2-enoate and subsequent in situ diastereoselective enolate oxidation with (+)-(camphorsulfonyl)oxaziridine gave tert-butyl (2R,3R,[small alpha]R)-2-hydroxy-3-(p-methoxyphenyl)-3-(N-benzyl-N-[small alpha]-methylbenzylamino)propanoate in >98% de. Subsequent N-benzyl deprotection to the primary [small beta]-amino ester via hydrogenolysis, oxazolidinone formation with C(2)-retention by treatment with diphosgene and chemoselective ester reduction furnishes (4R,5R)-cytoxazone. The synthesis of the C(5)-epimer, (4R,5S)-epi-cytoxazone in 44% overall yield, has also been completed via a protocol involving N-Boc protection of the primary [small beta]-amino ester, utilization of the N-Boc group to facilitate simultaneous C(2)-inversion and oxazolidinone formation, and subsequent reduction.     

从(-)-α-蒎烯合成(IR,3R)-(+)-反式菊酸甲酯

报道了以(-)-α-蒎烯为主要成分的松节油作原料,通过十四步反应合成了(1R,3R)-(+)-反式菊酸甲酯,每步反应的得率都在60%以上,总得率10.8%.反应操作方便,条件温和,对合成路线中的有些反应作了一些比较和讨论.化合物3-9都是新化合物.     

Enantioselective total syntheses of (+)-arborescidine A, (-)-arborescidine B, and (-)-arborescidine C

Described are the first enantioselective total syntheses of (+)-arborescidine A ((+)-1), (-)-arborescidine B ((-)-2), and (-)-arborescidine C ((-)-3), via routes that proceeded in five steps and 50% overall yield, eight steps and 61% overall yield, and nine steps and 51% overall yield, respectively, from 6-bromotryptamine (7). The syntheses feature the use of the Noyori catalytic asymmetric hydrogen-transfer reaction to introduce chirality in dihydro-beta-carbolines 6 and 8. On the basis of an ample precedent from Noyori's work, the reduction produces dihydro-beta-carbolines, and ultimately the natural products, possessing the R absolute configuration. The synthetic arborescidines displayed optical rotations that were opposite in sign those of the natural products, thereby supporting the S configuration for natural arborescidines A (1) and B (2) and the (3S,17S) configuration for natural arborescidine C (3). Our results are in agreement with the initial stereochemical assignment by Pa?s and co-workers, and are counter to their recently revised assignment.     

A chemoenzymatic dynamic kinetic resolution approach to enantiomerically pure (R)- and (S)-duloxetine

The synthesis of (R)-duloxetine is described. Dynamic kinetic resolution of β-hydroxynitrile rac-1 using Candida antarctica lipase B (CALB, N435) and ruthenium catalyst 6 afforded β-cyano acetate (R)-2 in high yield and in excellent enantioselectivity (98% ee). The subsequent synthetic steps were straightforward and (R)-duloxetine was isolated in 37% overall yield over 6 steps. The synthetic route also constitute a formal total synthesis of (S)-duloxetine.     

New method in synthesizing an optical active intermediate for (R,R)-formoterol

(R)-1-(4-Methoxyphenyl)propan-2-amine 2a,an optical active intermediate for (R,R)-formoterol,was synthesized from D- alanine in 65% overall yield by using a simple route,which contained protecting amino group,cyclization,coupling with Grignard reagent,reduction and deprotection.     

(R)-3-叔丁基二甲基硅氧丁基苯硫醚的合成方法改进

以4-(二甲氨基)吡啶为催化剂,通过(R)-3-叔丁基二甲基硅氧丁醇与甲磺酰氯之间的改进烷基磺酰化反应得到(R)-3-叔丁基二甲基硅氧丁基甲磺酸酯(2b,收率98%),2b再与苯硫酚钠反应生成(R)-3-叔丁基二甲基硅氧丁基苯硫醚(3,总收率89%)。2和3的结构经1H NMR,IR和MS表征。     

Enantio- and diastereoselective synthesis of (R,R)-beta-methoxytyrosine

The nonproteinogenic amino acid (2R,3R)-beta-methoxytyrosine, a constituent of several cyclic depsipeptide natural products, was synthesized in protected form (8) from a readily available cinnamate ester in four steps and 62% overall yield with a greater than 28:1 er and 19:1 dr. This method provides a highly efficient, enantio- and diastereoselective synthesis of an important amino acid.     

Total synthesis of (-)-(6S,7S,8S,9R,10S,2'S)-membrenone-A and (-)-(6S,7S,8S,9R,10S)- membrenone-B and structural assignment of membrenone-C

[reaction: see text] (-)-(6S,7S,8S,9R,10S,2'S)-Membrenone-A and (-)-(6S,7S,8S,9R,10S)-membrenone-B were prepared in 11 steps (3% and 2.4% overall yield, respectively). Key steps included a tin(II)-mediated aldol followed by a syn selective reduction, giving the C7-C9 stereocenters, a second chain extending aldol coupling, and a p-TsOH-promoted cyclization/dehydration giving the common gamma-dihydropyrone precursor. We have thus established that synthetic (-)-(6S,7S,8S,9R,10S,2'S)-membrenone-A, (-)-(6S,7S,8S,9R,10S)-membrenone-B, and (-)-(6S,7S,8S,9R,10S)-membrenone-C are the enantiomers of the natural products.     

Synthesis of （S） and （R）-tilisolol hydrochloride

Tilisolol hydrochloride 1,a non-selectiveβ-adrenoceptor blocker,was developed as a drug for the treatment of hypertension and angina pectoris.The optical active forms of 1,1a and 1b were synthesized from inexpensive phthalic anhydride 2 in eight steps with 13%(S) and 15%(R) overall yield.     

由(1S)-cis-菊酸合成(1R)-cis-二溴菊酸

拟除虫菊脂是在研究天然除虫菊脂化学的基础上发展起来的一类高效低毒,广谱杀虫剂。其中,溴氰菊脂是活性较高,光稳定性较好的一种菊脂类杀虫剂, 它是具有(IRcis.αs) 构型的单一光学异构体。 生产溴氰菊脂的关键中间体是IR-cis-)二溴菊脂。本文报道利用化学剪切法将(is)-cis-菊脂转化为(IR-cis-)二溴菊脂的新方法。     

Total synthesis of an immunosuppressive glycolipid, (2S,3S,4R)-1-O- (alpha-d-galactosyl)-2- tetracosanoylamino-1,3,4-nonanetriol

[reaction: see text] A practical and efficient total synthesis of (2S,3S,4R)-1-O-(alpha-d-galactosyl)-2-tetracosanoylamino-1,3,4-nonanetriol, OCH 1b, a potential therapeutic candidate for Th1-mediated autoimmune diseases, is described. The synthesis incorporates direct alkylation onto epoxide 5 and stereospecific halide ion catalyzed alpha-glycosidation reaction. A key intermediate 10 was obtained in only eight steps and 37% overall yield from commercially available d-arabitol 2, and the total synthesis of 1b was accomplished in 12 steps and 19% overall yield. This method will enable the synthesis of a variety of phytosphingolipids, especially that with the shorter sphingosine side chain than 1a, in a highly stereoselective manner.     

Synthesis of (R)-2-methyl-4-deoxy and (R)-2-methyl-4,5-dideoxy analogues of 6-phosphogluconate as potential inhibitors of 6-phosphogluconate dehydrogenase

The synthesis of (2R)-2-methyl-4,5-dideoxy and (2R)-2-methyl-4-deoxy analogues of 6-phosphogluconate is described. The synthetic strategy relies on the Evans aldol reaction for the installation of the chiral centres in the 2- and 3-positions. The selective phosphorylation at the primary alcohol function of (2R,3S)-3,6-dihydroxy-2-methylhexanoic acid benzyl ester (5) and (2R,3S,5S)-3,5,6-trihydroxy-2-methylhexanoic acid benzyl ester (20) was achieved with dibenzyl phosphochloridate and dibenzyl phosphoiodinate respectively, working at low temperature. (2R,3S)-3-Hydroxy-2-methyl-6-phosphonoxyhexanoic acid (9) was obtained in 25% overall yield from 4-benzyloxybutanol and (2R,3S,5S)-3,5-dihydroxy-2-methyl-6-phosphonoxyhexanoic acid (28) in 10% overall yield from L-malic acid.     

Total synthesis of (-)- and (+)-dysibetaine

Glycidamides 6R and 6S were elaborated to (R,R)- and (S,S)-dysibetaines (1R and 1S) by intramolecular alkylation and functional group modification in 23% overall yield. The absolute stereochemistry of natural dysibetaine was established as S,S by comparison of the optical rotation of the natural product with that of the synthetic materials.     

(1R,3S,4S)-2-苄氧羰基-2-氮杂双环[2.2.1]庚烷-3-羧酸的合成

以(R)-(+)-α-甲基苄胺为原料,依次经缩合,Diels-Alder反应,还原,Cbz-保护和水解反应,合成了抗丙肝新药HCV NS3/4A蛋白酶拟肽类抑制剂的重要中间体——(1R,3S,4S)-2-苄氧羰基-2-氮杂双环[2.2.1]庚烷-3-羧酸,总收率66%,其结构经1H NMR和ESI-MS确证。     

The Asymmetric Syntheses of Methyl <small>D</small>-Digitoxoside, <small>L</small>-Oleandrose and <small>L</small>-Cymarose from Methyl Sorbate, an Achiral Precursor

The addition of 4?eq of chloral to osmundalactone (4S,5R)-4 gave quantitative formation of the hemiacetal derivative (4S,5R)-8, which was treated with methane sulfonic acid to afford the intramolecular Micheal addition product (+)-(3S,4S,5R)-9 possessing a 3,4-cis-dihydroxy-δ-lactone in 78% overall yield from (4S,5R)-4. The obtained (+)-(3S,4S,5R)-9 was subsequently converted to methyl D-digitoxoside (pyranoside) (12) in 13% overall yield and methyl D-digitoxoside (furanoside) (12) in 20% overall yield. The reaction of benzyl-osmundalactone (4R,5S)-3 and MeOH in the presence of Amberlyst A-26 as a basic catalyst gave 3,4-trans-δ-lactone (－)-(3S,4R,5S)-20 in 28% yield and 3,4-cis-δ-lactone (－)-(3R,4R,5S)-21 in 45% yield. Dibal-H reduction of (－)-(3S,4R,5S)-20 followed by catalytic hydrogenation gave L-oleandrose (6) in 86% overall yield, while Dibal-H reduction of (－)-(3R,4R,5S)-21 followed by catalytic hydrogenation provided L-cymarose (7) in 85% overall yield.     

Terpenes in organic synthesis. 8. Synthesis of optically active (2R/S, 3S, 7R/S)-(-)-diprionyl acetate from (S)-(+)-3,7-dimethyl-1,6-octadiene

Conclusions A seven-stage synthesis has given optically active (2R/S, 3S, 7R/S)-2-acetoxy-3,7-dimethylpentadecane from the readily available (S)-(+)-3,7-dimethyl-1,6-octadiene, in an overall yield of 36%. The synthetic route utilizes all ten carbon atoms of the starting chiral diene.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1142–1146, May, 1988.     

Synthesis of (R)-curcumene and (R)-xanthorrizol based on 1,2-Aryl migration via phenonium ion

Solvolysis reaction of methyl (4S,5S)-4-(4'-methoxyphenyl)-5-tosyloxy-2(E)-hexenoate 5 in water-saturated MeNO(2) gave the 1,2-migration product, (4S,5S)-5-hydroxy-4-(4'-methoxyphenyl)-2-(E)-hexenoate 6 (55% yield), which was converted to methyl (R)-(4'-methylphenyl)hexanoate 11 in 25% overall yield (5 steps). Treatment of (R)-11 with MeLi gave tertiary alcohol congener 12, which was subjected to dehydration to afford (R)-(-)-curcumene 1. An introduction of hydroxyl group at meta-position of the aromatic ring in (R)-11 was achieved based on consecutive treatment [1) selective iodination, 2) conversion of aryl iodide to aryl boronate, 3) conversion of aryl boronate to phenol]. Thus obtained phenol (R)-16 was treated with MeLi to give tertiary alcohol congener 17, which was subjected to dehydration to afford (R)-(-)-xanthorrizol 2.     

Efficient and selective synthesis of (S,R,R,S,R,S)-4,6,8,10,16,18-hexamethyl-docosane via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction)

(S,R,R,S,R,S)-4,6,8,10,16,18-Hexamethyldocosane (1) was synthesized in 11% yield in 11 steps in the longest linear sequence from > or =98% pure (S)-beta-citronellal and 6 additional steps for the preparation of 11 in 23% yield from propene. Five of the six asymmetric carbon centers were generated catalytically and stereoselectively by the ZACA reaction (5 times), one lipase-catalyzed acetylation, and two chromatographic operations.     

Atropisomeric (R,R)-2,2'-Bi([2]paracyclo[2](5,8)quinolinophane) and (R,R)-1,1'-Bi([2]paracyclo[2](5,8)isoquinolinophane): synthesis, structural analysis, and chiroptical properties

Atropisomeric (R,R)-2,2'-bi([2]paracyclo[2](5,8)quinolinophane) [(R,R)-1] and (R,R)-1,1'-bi([2]paracyclo[2](5,8)isoquinolinophane) [(R,R)-2] have been prepared in moderate overall yield (17 and 9%, respectively) by a four-step sequence starting from (R)-(-)-4-amino[2.2]paracyclophane and (R)-(-)-4-carboxy[2.2]paracyclophane, respectively. The structures have been determined on the basis of NOE (1)H NMR analysis and molecular mechanics (MM) calculations performed with a Spartan02 program, using the MMF94s force field. A preliminary, qualitative analysis of the chiroptical properties of these two compounds has also been attempted. The main spectral data can be interpreted in terms of an almost planar 2,2'-bisquinoline chromophore inserted in a paracyclophane structure in the case of (R,R)-1, while in the case of (R,R)-2, the main role is played by a distorted 1,1'-bisisoquinoline chromophore. On the basis of the above structural results, a hypothesis about the enantioselection capability of these two molecules has also been formulated.