共查询到20条相似文献,搜索用时 15 毫秒
1.
D. Gautam 《Tetrahedron letters》2010,51(32):4199-4201
A stereoselective approach for the synthesis of (+)-(1R,2S,5S,7R)-2-hydroxy-exo-brevicomin from l-ascorbic acid has been described. The key steps are highly stereoselective nucleophilic addition reaction on aldehyde 8 and also a single pot transformation of 15 to (+)-(1R,2S,5S,7R)-2-hydroxy-exo-brevicomin. The later tandem reaction which involves the hydrogenation of double bond, debenzylation, MOM deprotection and bicyclic ketal formation was carried under Pd/C, H2 followed by acid treatment. 相似文献
2.
A convergent synthesis of (4R,15R,16R,21S)-rollicosin (1) and (4R,15S,16S,21S)-rollicosin (2) was accomplished. Hydroxy lactone 6a and/or 6b were synthesized from 4-pentyn-1-ol, and α,β-unsaturated lactone 7 was synthesized from γ-lactone 8 and 5-hexen-1-ol. Inhibitory activity of these compounds was examined with bovine heart mitochondrial complex I. 相似文献
3.
Stephen G. Davies James A. LeePaul M. Roberts Jeffrey P. StonehouseJames E. Thomson 《Tetrahedron letters》2012,53(9):1119-1121
The asymmetric synthesis of (−)-(S,S)-homaline was achieved in 8 steps from commercially available starting materials using the diastereoselective conjugate addition of the novel lithium amide reagent lithium (R)-N-(3-chloropropyl)-N-(α-methyl-p-methoxybenzyl)amide to methyl cinnamate to install the correct stereochemistry. Subsequent functional group manipulation of the resultant β-amino ester and Sb(OEt)3-mediated macrolactamisation was followed by homodimerisation to give (−)-(S,S)-homaline in 18% overall yield, representing the first asymmetric, and by far the most efficient synthesis of this natural product reported to date. 相似文献
4.
Darío Cuervo 《Journal of organometallic chemistry》2011,696(9):1861-1867
The complexes trans-[RuCl2(L){(S,S)-iPr-pybox}] ((S,S)-iPr-pybox = 2,6-bis[4′-(S)-isopropyloxazolin-2′-yl]pyridine, L = PMe3 (1), P(OMe)3 (2), PPh2(CH2CHCH2) (3), CNBn (5), CNCy (6) and MeCN (7)) have been synthesized by substitution of ethylene on the precursor trans-[RuCl2(η2-C2H4){(S,S)-iPr-pybox}]. This complex also reacts with cyclooctadiene (cod) or norbornadiene (nbd) and NaPF6, in refluxing methanol, giving the coordination compounds [RuCl(η4-cod){(S,S)-iPr-pybox}][PF6] (8) and [RuCl(η4-nbd){(S,S)-iPr-pybox}][PF6] (9). The structures of complexes [RuCl(CO)(PPh3)(H-pybox)][BF4] (H-pybox = 2,6-bis(dihydrooxazolin-2′-yl)pyridine) (4), 6 and 8, have been resolved by X-ray diffraction methods. The catalytic activity of the new complexes in transfer hydrogenation of acetophenone has also been examined. 相似文献
5.
A stereoselective synthesis of the pentaketide lactone (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone has been achieved. 相似文献
6.
Abhishek Dubey 《Tetrahedron letters》2009,50(26):3425-9290
A concise and highly efficient synthesis of l-arabino-[2R,3S,4R] and l-xylo-[2R,3S,4S]-C18-phytosphingosines has been achieved. The synthetic strategy features the Sharpless kinetic resolution and tethered aminohydroxylation as the key steps. 相似文献
7.
Gowravaram Sabitha E. Venkata Reddy M. Bhikshapathi J.S. Yadav 《Tetrahedron letters》2007,48(2):313-315
The total synthesis of (9S,12R,13S)-pinellic acid, a novel and potentially useful oral adjuvant, isolated from Pinelliae tuber has been accomplished. 相似文献
8.
The synthesis is described of the two enantiomerically pure isomers (+)-(3S,7S,10S)- and (+)-(3S,7S,10R)-3,7,10-trimethylboratr The structures were determined by 1H- and 13C-NMR spectroscopy. A method for increasing the enantiomeric purity by trimerization reactions of partially-resolved (S) propylene oxide is proposed. The reaction was studied from the kinetic viewpoint and interpreted according to a binomial probability scheme. The experimental findings point to a rapid growth in enantiomeric purity for the (SSS) trimer compared with the starting material, whilst no increase was found for the (SSR) trimer. 相似文献
9.
Sousuke Hara 《Tetrahedron》2004,60(37):8031-8035
The stereocontrolled synthesis of the protected (2S,3S)-N-methyl-5-hydroxyisoleucine, a component of halipeptins A and B with potent anti-inflammatory activity, has been achieved. The key steps include (i) installation of a double bond to bicyclic lactam 4 using N-tert-butyl phenylsulfinimidoyl chloride, (ii) highly exo-selective Michael reaction with lithium dimethylcuprate in the presence of chlorotrimethylsilane, and (iii) Ru-catalyzed oxidative deprotection of N,O-benzylidene acetal to the acid anhydride. 相似文献
10.
A total synthesis of (R,S)S-glucoraphanin (GRP) has been completed by a novel, simple and convenient method in high overall yield (17% over seven steps). The study describes a method for the synthesis of natural and unnatural (methylsulfinyl)alkyl glucosinolates (GLs) and also opens useful pathways to synthesize GRP as well as other sulfinyl GLs. 相似文献
11.
Paul Barraclough 《Tetrahedron letters》2005,46(27):4653-4655
A straightforward synthesis of (2S)-[3,3-2H2]-proline 1c and (2S,3R)- and (2S,3S)-[3-2H1]-proline, 1b and 1a, respectively, has been devised. The key step of the route to the latter compounds involves highly stereoselective hydrolysis of the silyl enol ethers 3 and 3a, respectively, with protonation (deuteriation) from the re-face of the silyl enol ether. 相似文献
12.
Ana Ardá 《Tetrahedron letters》2004,45(16):3241-3243
The first total synthesis of (2S,4S)-5,5-dichloroleucine has been achieved in 11 steps from l-pyroglutamic acid. A key step is the dichlorination process on the hydrazone of aldehyde 13 with CuCl2 in triethylamine. 相似文献
13.
A practical approach for the synthesis of the (2S,3S,4R)-trihydroxyazepane 1d has been reported. Starting from α-d-xylo-pentodialdose, readily available from d-glucose, the sequence involves Wittig olefination and reductive amination as key steps. 相似文献
14.
(S,R,S,R,S,R,S)- and (S,R,S,S,S,R,S)-octinaphthalenes were synthesized by oxidative coupling of (S,R,S)-quaternaphthalene, and differences due to axis chirality of (S,R,S,R,S,R,S)-, (S,R,S,S,S,R,S)-, (S,S,S,R,S,S,S)-, and (S,S,S,S,S,S,S)-octinaphthalenes were compared using the Rf values on TLC, specific optical rotations, 1H NMR chemical shifts of the hydroxy groups, and CD spectra. A clear CD additivity was found in the Δ? values of the 1La transition around 290 nm, which are proportional to the difference between the numbers of S and R binaphthalene units. 相似文献
15.
Kosuke Okuma Akira M. Ono Makoto Oba Masatsune Kainosho Tsutomu Terauchi 《Tetrahedron letters》2009,50(13):1482-163
We have developed a synthetic route for (2S,3R)- and (2S,3S)-[2-13C;3-2H] glutamic acids with high enantioselectivity. The key reactions in this synthesis are the asymmetric reduction of the 2,3-didehydroornithine derivative using the (S,S)-Et-DuPHOS-Rh catalyst and the oxidation of the δ-position by ruthenium catalysis. 相似文献
16.
Erik A.A. Wallén Johannes A.M. Christiaans Jukka Gynther Jouko Vepsäläinen 《Tetrahedron letters》2003,44(10):2081-2082
The synthesis of (2S,5S)-Boc-5-tert-butylproline ethyl ester via the addition of tert-butylcuprate to (2S)-N-Boc-Δ5-dehydroproline ethyl ester, formed from (2S)-N-Boc-5-methoxyproline ethyl ester, gives an excellent yield of 94% and a high diastereoselectivity (2S,5S):(2S,5R) 78:22. This synthesis opens up a new synthetic route to (2S,5S)-5-tert-butylproline, which is a useful, conformationally rigid, analogue of l-proline. 相似文献
17.
This article reports the design and facile synthesis of novel chiral six-membered PNA analogues (2S,5R/2R,5S)-1-(N-Boc-aminoethyl)-5-(thymin-1-yl)pipecolic acid, aepipPNA IV that upon incorporation into standard aegPNA sequences effected stabilization of complexes with complementary target DNA. Substitution of aegPNA unit by the designed monomer at the C-terminus was more effective than substitution at N-terminus. The stabilizing behaviour improved with degree of substitution and was found to be dependent on their relative positions in the sequence. The six-membered piperidine ring in the design may freeze the rigid chair conformations and the relative stereochemistry of the substituents may in effect direct the complex formation with DNA/RNA by sequence-specific nucleobase recognition. In the present aepipPNA analogues, the l-trans stereochemical disposition of the substituents seems to lead to the favorable pre-organization of the PNA oligomers for complex formation with DNA. The results reported here further expand the repertoire of cyclic PNA analogues. 相似文献
18.
16R-Bromopregnane-3S,20S-diol reacted with potassium t-butoxide to afford androst-16-en-3S-ol in a moderate yield via fragmentation reaction. The latter is a key intermediate for the synthesis of 5α-androst-16-en-3-one, as boar sex pheromone, and other steroidal drugs. In addition, 16R,20S-epoxypregnane-3S-ol was also obtained as a major product by changing the reaction solvent. 相似文献
19.
?rt Malavaši?Uroš Grošelj Amalija Golobi?Jure Bezenšek Branko Stanovnik Katarina Stare Jernej WaggerJurij Svete 《Tetrahedron: Asymmetry》2011,22(6):629-640
Eleven (S)-1,6-dialkylpiperazine-2,5-diones and five (3S,6S)-1,3,6-trialkylpiperazine-2,5-diones were prepared in three steps from the corresponding (S)-α-amino acid esters comprising of reductive N-alkylation, N-acylation and cyclisation. The synthesis of (S)-1,6-dialkylpiperazine-2,5-diones has a broad scope allowing preparation of diketopiperazines with primary and secondary alkyl groups at N(1), while the synthesis of (3S,6S)-1,3,6-trialkylpiperazine-2,5-diones is limited to compounds with primary alkyl groups at N(1). Reductive alkylation of amino acid ester hydrochlorides by catalytic hydrogenation in the presence of a carbonyl compound proved to be a simple, efficient and general method for the preparation of stable (storable) α-alkylamino acid ester hydrochlorides. The structures of the novel compounds were determined by NMR and X-ray diffraction. 相似文献
20.
Jaru Taechalertpaisarn 《Tetrahedron letters》2010,51(44):5822-5826
A new pyrrolidinyl peptide nucleic acid (PNA) comprising of an alternate sequence of 4′-nucleobase-modified proline with (2′R,4′S) configuration and a (1S,2S)-2-aminocyclopentanecarboxylic acid [(2′R,4′S)-acpcPNA] backbone was synthesized and its DNA-, RNA- and self-pairing properties studied. Tm and CD studies suggested that the (2′R,4′S)-acpcPNA forms antiparallel hybrids to DNA and RNA with high sequence and direction specificity. The stability of these hybrids is comparable to those of the (2′R,4′R)-acpcPNA hybrids previously reported by our group. On the other hand, experiments with a self-complementary sequence indicated that the new (2′R,4′S)-acpcPNA forms a more stable antiparallel self-hybrid than (2′R,4′R)-acpcPNA. 相似文献