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.     

Chemoenzymatic synthesis of (S)-hexafluoroleucine and (S)-tetrafluoroleucine

We have developed a short chemoenzymatic synthesis for both (S)-5,5,5,5',5',5'-hexafluoroleucine (Hfl) and (S)-5,5,5',5'-tetrafluoroleucine (Qfl) on gram scale. Qfl was incorporated into a peptide using standard solid-phase peptide synthesis protocols to measure its helix propensity. The helix propensity for Qfl is 0.68 kcal.mol-1 more favorable compared to Hfl.     

Mechanochromism of Ag(I) complexes with iPrNHC(S)NHP(S)(OiPr)2

Reaction of the potassium salt of iPrNHC(S)NHP(S)(OiPr)(2) (HL) with AgPF(6) leads to the hexanuclear [{Ag(3)(iPrNHC(S)NP(S)(OiPr)(2)-S,S')(3)}(2)] ([(Ag(3)L(3))(2)]) complex. The reversible conversion between yellow-emitting ([(Ag(3)L(3))(2)]) and blue-emitting ([Ag(3)L(3)]) materials on grinding and recrystallization was established. [Ag(3)L(3)] was also prepared by a mechanically induced solid-state reaction.     

Synthesis of dolichol-type (S)-hexa- and (S)-heptaprenols

(R)-1-Phenysulfonyl-2-methylbutan-4-ol has been used as starting material for the stepwise synthesis of the dolichol-related hexa- and heptaprenols (S)-3,7, 11,15,19,23-hexamethyltetraeicosa-6Z,10Z,14E,18E,22-pentaene-1-ol and (S)-3,7, 11,15,19,23,27-heptamethyloctaeicosa-6Z,10Z,14E,18E,22E,26-hexaen-1-ol.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2052–2056, September, 1989.     

(4S)-苯氧基-(S)-脯氨酸催化直接不对称羟醛缩合反应

N-乙氧羰基-(4R)-羟基-(S)-脯氨酸甲酯与苯酚的Mitsunobu反应给出N-乙氧羰基-(4S)-苯氧基-(S)-脯氨酸甲酯,后者经皂化和盐酸水解后得标题氨基酸.这一化合物(5 mol%)对映选择性催化丙酮和取代苯甲醛的羟醛缩合反应,产率67.4%～89.9%,ee最高达76.5%.     

S(1S) production following electron impact on thiophosgene (Cl2CS)

A special xenon matrix detector has been used to study the production of S(1S) following controlled electron impact on thiophosgene (Cl2CS) targets over an electron energy range from threshold to 400 eV. Time-of-flight spectroscopy has been used to measure S(1S) fragment kinetic energies. Fragments with energies in excess of 1 eV have been observed. The absolute cross section for S(1S) production reaches a maximum of [1.05+/-0.35] x 10(-18) cm2 at approximately 125 eV impact energy. Two different fragmentation processes, involving triplet and singlet excited states of the parent Cl2CS molecule, have been identified.     

Concise asymmetric synthesis of (5S, 6S)- aeginetolide and (5S)- dihydroactinidiolide

An asymmetric deprotonation reaction allows for short syntheses of the lactones (5S, 6S)- Aeginetolide (1) and (5S)-Dihydroactinidiolide (2).     

Enantioselective Synthesis of (1R,2S) and (1S,2S) Dehydrocoronamic Acids

Thanks to the successive use of two esterases with different regioselectivities and conventional organic chemistry we have synthesized (1R,2S) and (1S,2S) dehydrocoronamic acids.     

Interconversion of (S)-glutamate and (2S,3S)-3-methylaspartate: a distinctive B(12)-dependent carbon-skeleton rearrangement

The interconversion of (S)-glutamate and (2S,3S)-3-methylaspartate catalyzed by B(12)-dependent glutamate mutase is discussed using results from high-level ab initio molecular orbital calculations. Evidence is presented regarding the possible role of coenzyme-B(12) in substrate activation and product formation via radical generation. Calculated electron paramagnetic resonance parameters support experimental evidence for the involvement of substrate-derived radicals and will hopefully aid the future detection of other important radical intermediates. The height of the rearrangement barrier for a fragmentation-recombination pathway, calculated with a model that includes neutral amino and carboxylic acid substituents in the migrating glycyl group, supports recent experimental evidence for the interconversion of (S)-glutamate and (2S,3S)-3-methylaspartate through such a pathway. Our calculations suggest that the enzyme may facilitate the rearrangement of (S)-glutamate through (partial) proton-transfer processes that control the protonation state of substituents in the migrating group.     

Extending the coordination chemistry of molecular P(4)S(3): the polymeric Ag(P(4)S(3))(+) and Ag(P(4)S(3))(2)(+) cations

Upon reacting P(4)S(3) with AgAl(hfip)(4) and AgAl(pftb)(4) [hfip = OC(H)(CF(3))(2); pftb = OC(CF(3))(3)], the compounds Ag(P(4)S(3))Al(hfip)(4) 1 and Ag(P(4)S(3))(2)(+)[Al(pftb)(4)](-) 2 formed in CS(2) (1) or CS(2)/CH(2)Cl(2) (2) solution. Compounds 1 and 2 were characterized by single-crystal X-ray structure determinations, Raman and solution NMR spectroscopy, and elemental analyses. One-dimensional chains of [Ag(P(4)S(3))(x)](infinity) (x = 1, 1; x = 2, 2) formed in the solid state with P(4)S(3) ligands that bridge through a 1,3-P,S, a 2,4-P,S, or a 3,4-P,P eta(1) coordination to the silver ions. Compound 2 with the least basic anion contains the first homoleptic metal(P(4)S(3)) complex. Compounds 1 and 2 also include the long sought sulfur coordination of P(4)S(3). Raman spectra of 1 and 2 were assigned on the basis of DFT calculations of related species. The influence of the silver coordination on the geometry of the P(4)S(3) cage is discussed, additionally aided by DFT calculations. Consequences for the frequently observed degradation of the cage are suggested. An experimental silver ion affinity scale based on the solid-state structures of several weak Lewis acid base adducts of type (L)AgAl(hfip)(4) is given. The affinity of the ligand L to the silver ion increases according to P(4) < CH(2)Cl(2) < P(4)S(3) < S(8) < 1,2-C(2)H(4)Cl(2) < toluene.     

Asymmetric synthesis of anti-(2S,3S)- and syn-(2R,3S)-diaminobutanoic acid

Conjugate addition of homochiral lithium N-benzyl-N-alpha-methylbenzylamide to tert-butyl (E)-cinnamate or tert-butyl (E)-crotonate and in situ amination with trisyl azide results in the exclusive formation of the corresponding 2-diazo-3-amino esters in > 95% de. Amination of the lithium (E)-enolates of tert-butyl (3S,alphaR)-3-N-benzyl-N-alpha-methylbenzylamino-3-phenylpropanoate or tert-butyl (3S,alphaS)-3-N-benzyl-N-alpha-methylbenzylaminobutanoate with trisyl azide gives the (2R,3R,alphaR)- and (2S,3S,alphaS )-anti-2-azido-3-amino esters in good yields and in 85% de and > 95% de respectively. Alternatively, tert-butyl anti-(2S,3S,alphaS)-2-hydroxy-3-N-benzyl-N-alpha-methylbenzylaminobutanoate may be converted selectively to tert-butyl anti-(2S,3S,alphaS)-2-azido-3-N-benzyl-N-alpha-methylbenzylaminobutanoate by aziridinium ion formation and regioselective opening with azide. Deprotection of tert-butyl (2S,3S,alphaS)-2-azido-3-aminobutanoate via Staudinger reduction, hydrogenolysis and ester hydrolysis furnishes anti-(2S,3S)-diaminobutanoic acid in 98%, de and 98% ee. The asymmetric synthesis of the diastereomeric syn-(2R,3S)-diaminobutanoic acid (98% de and 98% ee) was accomplished via functional group manipulation of tert-butyl anti-(2S,3S,alphaS)-2-hydroxy-3-N-benzyl-N-alpha-methylbenzylaminobutanoate in a protocol involving azide inversion of tert-butyl (2S,3S)-2-mesyloxy-3-N-Boc-butanoate and subsequent deprotection.     

Reversible disulfur monoxide (S2O)-forming retro-Diels-Alder reaction. disproportionation of S2O to trithio-ozone (S3) and sulfur dioxide (SO2) and reactivities of S2O and S3

5,6-Di-tert-butyl-2,3,7-trithiabicyclo[2.2.1]hept-5-ene 7-endo-oxide (4) was prepared by addition of S(2)Cl(2) to 3,4-di-tert-butylthiophene 1-oxide (3) in high yield. The oxidation of 4 with dimethyldioxirane gave a 7:1 isomeric mixture of 5,6-di-tert-butyl-2,3,7-trithiabicyclo[2.2.1]hept-5-ene 2-endo-7-endo-dioxide (5a) and 2-exo-7-endo-dioxide (5b) quantitatively. The thermally labile 5 was shown to undergo a retro-Diels-Alder reaction that produces S(2)O and 3 in a reversible way. The resulting S(2)O was trapped by Diels-Alder reactions with dienes to give 3,6-dihydro-1,2-dithiin 1-oxides in good yields. In the absence of the dienes, S(2)O disproportionates to SO(2) and S(3), and the resulting S(3) underwent a 1,3-dipolar cycloaddition with 3 on its syn-pi-face with respect to the S[double bond]O bond to give a trithiolane derivative, whereas in the presence of excess norbornene, it produced the 1,3-dipolar cycloadduct with norbornene in good yield. Thus, the retro-Diels-Alder reaction of 5 functions as an S(2)O and S(3) source. DFT calculations at the B3LYP/6-311+G(3df,2p) level were carried out in order to explain why S(2)O disproportionates to SO(2) and S(3) and why S(2)O acts as a dienophile and not a 1,3-dipole, whereas O(3) and S(3) serve as 1,3-dipoles.     

(S)-美托洛尔的不对称合成

用自制的(S,S)-Salen Co(Ⅲ)OAc催化剂水解动力学拆分外消旋环氧氯丙烷得到高光学纯的(S)-3-氯-1,2-丙二醇和较高光学纯的(R)-环氧氯丙烷。 以(S)-3氯-1,2-丙二醇为手性原料和4-(2-甲氧基乙基)苯酚缩合,再与氯化亚砜反应得环状亚硫酸酯,最后和异丙胺反应得(S)-美托洛尔,光学纯度大于99%。 另外以(R)-环氧氯丙烷为手性原料和4-(2-甲氧基乙基)苯酚反应,再与异丙胺作用得到(S)-美托洛尔,光学纯度大于92%。 (S)-美托洛尔的总收率为53.9%,结构经IR、1H NMR、13C NMR和MS测试技术确证。 该路线原料利用率高,拆分后的2种产物均能用于目标化合物的合成。     

Determination of (34)S:(32)S ratios by FTIR spectroscopy

A new method for determining (34)S:(32)S ratios using Fourier transform infrared spectroscopy has been developed. The four sulphur-containing gases SCO, H(2)S, SF(6) and SO(2) are assessed as possible compounds for the spectroscopic measurements, from which, after a consideration of available lines showing a clear isotopic shift and also of possible synthetic routes to the gas starting from a range of natural sample types, SO(2) was selected for further development of the instrumental method for the isotopic ratio determination. Sulphur in the samples present as the element, as metal sulphides or as organosulphur compounds, is converted by heating with V(2)O(5) into gaseous SO(2), and a part of the 518 cm(-1) band is recorded in the absorbance mode. The optimisation of instrumental parameters and of the chemical reaction conditions is described, and the results from the application of the method to the measurement of the level of enrichment of (34)S in a soil fungus are presented. The agreement between results at the natural abundances of 4.2% was better than 0.04% absolute for a sample size of 1.5 mg of sulphur.     

Total synthesis of (S)-(+)-curcudiol, and (S)-(+)- and (R)-(-)-curcuphenol.

A highly enantioselective synthesis of the versatile chiral synthons possessing one stereogenic center, (S)- and (R)-4-aryl-5-hydroxy-(2E)-pentenoate (3) was achieved based on the enzymatic reaction of (+/-)-3 with commercially available lipases MY-30 or OF-360 from Candida rugosa. Application of (S)-3 and (R)-3 to the total syntheses of(S)-curcuphenol (1), (S)-curcudiol (2), and (R)-curcuphenol (1), respectively, is described.     

Exploratory synthesis in molten salts: role of flux basicity in the stabilization of the complex thiogermanates Cs(4)Pb(4)Ge(5)S(16), K(2)PbGe(2)S(6), and K(4)Sn(3)Ge(3)S(14)

The influence of the Lewis basicity of alkali polysulfide fluxes (A(2)S(x)) (A = alkali) as a function of x on the respective reactivities of Pb and Sn with Ge was studied and found to be strong. Cs(4)Pb(4)Ge(5)S(16), K(2)PbGe(2)S(6), and K(4)Sn(3)Ge(3)S(14) could be prepared only under low basicity with S/A(2)S ratios of > or =11. These compounds display complex frameworks and are semiconductors. Cs(4)Pb(4)Ge(5)S(16) is luminescent with red emission.     

Deprotonierte Dithiocarbaminsäureester als Thiolat-S-Donor-Liganden. Strukturen von Ph(H)NC(S)SMe,Co(PhNC(S)SMe)3 und Cu6(PhNC(S)SMe)6

Deprotonated Dithiocarbamic Acid Esters as Thiolate S-Donor Ligands. Structures of Ph(H)NC(S)SMe, Co(PhNC(S)SMe)₃, and Cu₆(PhNC(S)SMe)₆ The reaction of N-phenyl-S-methyldithiocarbamate, PhN(H)C(?S)SMe, ( 1 ) with cobalt(II) and copper(II) salts yields the monomeric compound Co^III(PhNC(S)SMe)₃ ( 2 ) and the hexameric compound Cu₆^I(PhNC(S)SMe)₆ ( 3 ). These complexes contain the negatively charged imino-thiolate ligand PhN?C(? S)SMe, which has been formed by deprotonation of 1 . The crystal structures of 1 – 3 have been determined. 1 forms centrosymmetrical dimers through N? H …? S bridge bonds, the conformation in the solid state and in solution is Z,E′. Co^III shows in 2 a trigonal-antiprismatic coordination, with the ligands acting as N,S-chelates. 3 contains an octahedral Cu₆-core with Cu …? Cu-distances ranging from 276.3(5) to 305.7(4) pm. Each copper center is trigonally coordinated to one nitrogen and two sulfur atoms of three different ligands. Crystal data: 1 , triclinic, space group P1 , a = 590.5(6), b = 869.0(1), c = 968.5(9) pm, α = 67.29(8), β = 78.44(8), γ = 81.64(9)°, Z = 2, 1 775 reflections, R(R_w) = 0.0317(0.032). 2 , orthorhombic, space group Pbca, a = 978.0(2), b = 1 842.9(4), c = 3 059.7(6) pm, Z = 8, 1 129 reflections, R(R_w) = 0.0997(0.0886). 3 , monoclinic, space group P2₁/c, a = 1 363.1(3), b = 1 342.8(3), c = 1 671.9(3) pm, β = 103.48°, Z = 2, 1 374 reflections, R(R_w) = 0.0708(0.0617).     

Asymmetric Synthesis of (R)-and (S)-Moprolol

A simple and effective procedure for the enantioselective synthesis of (R)-and (S)-moprolol was described.The key step was the asymmetric synthesis of enantiopure (R)-and (S)-guaifenesin,which were synthesized from enantioenriched (R)-3-chloro-1,2-propanediol and (S)-epichlorohydrin via kinetics of hydrolysis resolution of racemic epichlorohydrin by chiral Salen-CoIIII complex.The e.e.values of both the optical compounds were above 98%,and the chemical structures of the target compounds were confirmed by 1H NMR,13C NMR,IR,and MS.     

Preparation and X-ray structures of Cu(I), Ni(II), and Pd(II) (N,S) complexes of the monoanion [(tBuN)(S)P(mu-N(t)Bu)2P(S)(NH(t)Bu)]- and a Pt(II) (S,S') complex of the dianion [((t)BuN)(S)P(mu-N(t)Bu)2P(S)(N(t)Bu)]2-

The metathetical reactions of the lithium derivative of the monoanion [((t)BuN)(S)P(mu-N(t)Bu)(2)P(S)(NH(t)Bu)](-) (L) with CuCl/PPh(3), NiCl(2)(PEt(3))(2), PdCl(2)L'(2) (L' = PhCN, PPh(3)), and PtCl(2)(PEt(3))(2) produced the complexes (PPh(3))CuL (5), NiL(2) (6), PdCl(L)(PPh(3)) (7), PdL(2) (8), and Pt(PEt(3))(2)[((t)BuN)(S)P(mu-N(t)Bu)(2)P(S)(N(t)Bu)] (9). The X-ray structures of 5, 6, and 8 reveal a N,S-coordination for the chelating monoanion L with the metal centers in trigonal planar, tetrahedral, and square planar environments, respectively. By contrast, the dianionic ligand in the square planar Pt(II) complex 9 is S,S'-chelated to the metal center. (31)P NMR spectra readily distinguish between the N,S and S,S' bonding modes, and, on that basis, N,S chelation is inferred for the Pd(II) complex 7. Crystal data: 5, monoclinic, P2(1)/c, a = 19.175(4) A, b = 20.331(4) A, c = 10.017(6) A, beta = 91.79(3) degrees, V = 3903(2) A(3), and Z = 4; 6, orthorhombic, Pbcn, a = 14.298(5) A, b = 15.333(5) A, c = 24.378(5) A, beta = 90.000(5) degrees, V = 5344(3) A(3), and Z = 4; 8, monoclinic, P2(1)/n, a = 13.975(3) A, b = 14.283(3) A, c = 15.255(4) A, beta = 116.565(18) degrees, V = 2723.5(11) A(3), and Z = 2; 9, monoclinic, P2(1)/n, a = 12.479(6) A, b = 21.782(7) A, c = 17.048(5) A, beta = 100.30(3) degrees, V = 4559(3) A(3), and Z = 4.     

Synthesis of (2S,4S)- and (2S,4R)-5-fluoroleucine and (2S,4S)-[5,5-2H2]-5-fluoroleucine

Syntheses of (2S,4S)- and (2S,4R)-5-fluoroleucine, and, and of (2S,4S)-[5,5-(2)H(2)]-5-fluoroleucine, have been completed. The methodology allows these compounds to be prepared in sufficient quantities for incorporation by solid-state protein synthesis into strategic sites in proteins for folding studies. X-ray structures of the epimers and have been obtained and show the presence of conformational isomerism. The torsion angles between the F-C bond and the main chain are compared with values found in a mutant of the protein ubiquitin in which (2S,4S)-5-fluoroleucine replaces leucine residues 50 and 67 in the native protein.