Synthesis of L-2,3-Diaminopropionic Acid,a Siderophore and Antibiotic Precursor

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The vibrational spectra, molecular structure and conformation of organic azides Part III. 2,3-Diazido-1,3-butadiene

A sample of 2,3-diazido-1,3-butadiene has been synthesized from 1,4-dibromo-2-butyne and tetramethylguanidinium azide. The highly explosive sample has been studied by gaseous electron diffraction and by IR spectroscopy. Only incomplete Raman spectra have been recorded due to sample decomposition in the laser beam. The title compound is found to be planar with the CNN angle equal to 114.5°, oriented syn to the adjacent C=C double bond; the NNN angle is ca. 167°, oriented anti to the C---N bond. The following bond distances (r_a) are obtained: N---N(N), 114.1; N---N(C), 124.2; C---N, 143.2; C=C 134.8; and C---C, 148.5 pm. The vibrational spectra are tentatively assigned in terms of C_2h molecular symmetry, supported by force constant calculations.     

A Metal-organic Framework Constructed from a Rare Rod-shaped Secondary Building Unit and Its Highly Efficient Photocatalytic Activity

A new Cu(Ⅱ) coordination polymer,{[Cu_3(oba)_2(μ~3-OH)_2(H_2O)_2].6H_2O}_n(H_2 oba=4,4'-oxydibenzoic acid),was synthesized by the solvothermal route and characterized by IR,TGA and XRD.The complex crystallizes in the monoclinic system,space group P2_1/c with a=5.957(6),b=29.746(3),c=9.351(7) A,β=125.709(4)°,V=1345.4(2) A~3,Z=2,C_(28)H_(36)Cu_3O_(20),M_r=883.09,D_c=1.913 g/cm~3,F(000)=782,μ=2.427 mm~(-1),R=0.0780 and wR=0.1688 for 3120 observed reflections with I 2σ(I).The complex forms a 3D framework based on rare infinite rod-shaped secondary building units(SBUs),and C-H…π interactions play an important role in stabilizing the 3D supramolecular architecture.It shows excellent catalytic activities for the degradation of safranin O(SO) and methylene blue(MB) dyes in aqueous solution under UV light irradiation.Furthermore,the apparent rate constants have also been investigated.     

Synthetic Studies of Et-743, Preparation of A Racemic Amino Alcohol Precursor

A mild two-step method was used to cleave the lactam ring of the tricyclic intermediate 1. A key racemic amino alcohol precursor 5 for the construction of Et-743 skeleton was synthesized from 1 through four steps in total yield of 47%.     

N—乙基—N—苄基苯胺合成方法的改进

以苯胺和乙醇为原料，采用ＲａｎｅｙＮｉ为催化剂，合成了Ｎ－乙基苯胺，再在相转移催化剂作用下，经苄基化反应得到标题化合物，第一步合成方法的收率比通常方法的收率提高约３０％。     

Phosphinothricin as a Building Unit for Oligopeptides

Abstract

Peptides with N-terminal homoalanin-4-yl (methyl)phosphinic acid (phosphinothricin, 1) can be synthesized by means of the carbodiimide method. Advantageously the carbobenzyloxy (Z-) group is used as amino protecting group, while protection of the phosphinic acid is not necessary. The key-step of this procedure is the intermediate formation of the cyclic phosphinic acid-carboxylic acid - anhydride 2, which is attacked by N-nucleophiles, such as amino acid esters, selectively at the carbonyl function. On the other hand, reaction of 2 with alcohols yields phosphinothricin-P-esters with a free carboxylic group. These compounds are valuable starting materials for further peptide syntheses.     

2,3-Dichlorobicyclo[2.2.1]hepta-2,5-diene: A Convenient Precursor of Norbornadiene-2,3-diynes

Norbornadienes that feature the properties of norbornadiene and of the ene-diyne in the same molecule have been prepared via a simple and high-yielding route starting fromdichlorobicyclo[2.2.1]hepta-2,5-diene (1).     

Building a Better Halide Receptor: Optimum Choice of Spacer,Binding Unit,and Halosubstitution

Quantum calculations are used to measure the binding of halides to a number of bipodal dicationic receptors, constructed as a pair of binding units separated by a spacer group. A number of variations are studied. A H atom on each binding unit (imidazolium or triazolium) is replaced by Br or I. Benzene, thiophene, carbazole, and dimethylnaphthalene are considered as spacer groups. Each receptor is paired with halides F^?, Cl^?, Br^?, and I^?. Substitution with I on the binding unit yields a large enhancement of binding, as much as 13 orders of magnitude; a much smaller increase occurs for substitution with Br. Imidazolium is a more effective binding agent than is triazolium. Benzene and dimethylnaphthalene represent the best spacers, followed by thiophene and carbazole. F^? binds much more strongly than do the other halides, which obey the order Cl^?>Br^?>I^?.     

Synthetic Chemistry and Function of Bacterial Cell Surface Glycoconjugates

Typical bacterial glycoconjugates are known to stimulate immunological systems of higher animals and thereby play important roles in the primary defense of animals against bacterial infection. Lipopolysaccharide (LPS) of gram‐negative bacteria is a representative of such glycoconjugates. LPS was first discovered as a potent bacterial toxin and named endotoxin but was soon found to exhibit immunostimulating activity. By the use of our synthetic pure preparations, the lipophilic partial structure of LPS, designated lipid A, proved to be the active entity responsible for both endotoxic and immunostimulating activities of LPS. This paper deals with our recent chemical synthesis and functional study of lipid A and related compounds. Synthesis is described of its various structural analogues, radio‐labeled compound and Re‐type LPS that contains two additional sugar moieties linked to lipid A.     

2,3,4,5-四取代-顺-2,3-二氢呋喃立体选择性合成方法的研究

研究了3种合成2甲氧羰基3芳基4乙酰基5甲基顺2,3二氢呋喃(7)的方法.方法1:用甲氧羰基亚甲基三苯基胂(5)与3(取代苯甲叉)2,4戊二酮(6)反应;方法2:用溴化甲氧羰基甲基三苯基胂(4)在碳酸钾存在下与戊二酮6反应;方法3(分步一锅法):三苯基胂(2)与溴代乙酸甲酯(3)加热反应,生成的产物不经分离,冷却至室温,加入碳酸钾和6继续反应.     

Sonogashira Coupling Offers a New Synthetic Route to Thieno[2,3-c]pyrazoles

Abstract

1,3-Disubstituted-5-chloro-4-iodopyrazoles are selectively coupled with phenylacetylene under typical Sonogashira reaction conditions [PdCl₂(PPh₃)₂, CuI, Et₃N, dimethylformamide (DMF)] to obtain the corresponding 5-chloro-4-(phenylethynyl)pyrazoles in good yield. The latter are smoothly cyclized with Na₂S in DMF into the corresponding thieno[2,3-c]pyrazoles. Detailed spectroscopic investigations (¹H, ¹³C, and ¹⁵N NMR, mass, and infrared) of all compounds are reported.     

Synthetic Studies of a Didemnin B Analog Based on a 2,3‐Diamino Sugar Scaffolding

Reductive amination, amide formation using BOP [(1H‐1,2,3‐benzotriazol‐1‐yloxy)tris(dimethylamino)‐phosphonium hexafluorophosphate] and esterification via DCC (dicyclohexylcarbodiimide) were the key synthetic steps to generate an advanced intermediate in the preparation of a didemnin B analog based on a sugar scaffolding ( 2 ). This analog should provide insight into the bioactive conformation of didemnin B.     

Syntheses and Characterization of Two Adducts Based on 2,3-Diaminoquinoxaline with Imidazoquinoxaline as Precursor

The reactions of imidazoquinoxaline and 1,3,5-H3 btc acid under different condition have been investigated. The different degree of hydrolysis reaction leads to two different adducts being produced, namely, [(Hdiam Quin)+(H2btc)-](1), and [(diam Quin)4(Imi Quin)·4H2O](2). Both compounds were characterized by X-ray crystallography. Crystal data for 1: monoclinic, space group Pn with a = 9.868(2), b = 5.3172(11), c = 15.387(3) ?, β = 91.10(3)o, C17H14N4O6, Mr = 370.32, V = 807.2(3) ?3, Z = 2, Dc = 1.524 g/cm~3, μ(Mo Kα) = 0.118 mm-1, F(000) = 384, the final R = 0.0385 and w R = 0.0869 for 2294 observed reflections(I 2σ(I)). Crystal data for 2: triclinic, space group P1 with a = 9.825(2), b = 14.144(3), c = 16.054(3) ?, α = 101.06(3), β = 102.55(3), γ = 92.46(3)o, C_(44)H40N_(20)O_4, Mr = 912.96, V = 2128.8(7) ?3, Z = 2, Dc = 1.424 g/cm~3, μ(Mo Kα) = 0.099 mm-1, F(000) = 952, the final R = 0.0554 and w R = 0.1662 for 6563 observed reflections(I 2σ(I)). X-ray diffraction analysis reveals that compound 1 is a salt. Imidazoquinoxaline was wholly hydrolyzed into 2,3-diaminoquinoxaline and protonated as a cation with H2btc-acting as an anion. However, in compound 2, the imidazoquinoxaline is only partly hydrolyzed, and the resulting 2,3-diaminoquinoxaline forms adduct with the intacted imidazoquinoxaline. Both are further aggregated into 3D frameworks by strong hydrogen bonding even π-π interactions.     

A Short,Efficient, Multigram Synthetic Route to 2,3-Dimethylfuran and Some of its 2-Substituted Derivatives

A laboratory, multigram (1000 g in an hour) preparation procedure for 2,3-dimethylfuran, based on the frequently repeated thermal cyclization of (Z) 3-methyl-2-penten-4-yn-1-ol, as well as its subsequent formylation, acetylation and oxidation is described.