(SR/RS)-cyclohexanyl PNAs: conformationally preorganized PNA analogues with unprecedented preference for duplex formation with RNA

PNA oligomers H-GTAGATCAT-lys-NH2 with cis-(1S,2R/1R,2S)-cyclohexyl-T (III) in the backbone form PNA:RNA duplexes with Tm approximately 30-50 degrees C higher than that of PNA:DNA duplexes. In comparison, cis-(1S,2R/1R,2S)-cyclopentyl PNA-T (IV) form highly stable duplexes with both RNA and DNA without discrimination.     

(1S,2R/1R,2S)-cis-cyclopentyl PNAs (cpPNAs) as constrained PNA analogues: synthesis and evaluation of aeg-cpPNA chimera and stereopreferences in hybridization with DNA/RNA

Conformationally constrained chiral PNA analogues were designed on the basis of stereospecific imposition of a 1,2-cis-cyclopentyl moiety on an aminoethyl segment of aegPNA. It is known that the cyclopentane ring is a relatively flexible system in which the characteristic puckering dictates the pseudoaxial/pseudoequatorial dispositions of substituents. Hence, favorable torsional adjustments are possible to attain the necessary hybridization-competent conformations when the moiety is imposed on the conventional PNA backbone. The synthesis of the enantiomerically pure 1,2-cis-cyclopentyl PNA monomers (10a and 10b) was achieved by stereoselective enzymatic hydrolysis of a key intermediate ester 2. The chiral (1S,2R/1R,2S)-aminocyclopentylglycyl thymine monomers were incorporated into PNA oligomers at defined positions and through the entire sequence. Hybridization studies with complementary DNA and RNA sequences using UV-Tm measurements indicate that aeg-cpPNA chimera form thermally more stable complexes than aegPNA with stereochemistry-dependent selective binding of cDNA/RNA. Differential gel shift retardation was observed on hybridization of aeg-cpPNAs with complementary DNA.     

(1S,2R/1R,2S)-ainocyclohexyl glycyl thymine PNA: synthesis,monomer crystal structures,and DNA/RNA hybridization studies

[structure: see text] The synthesis of ethyl cis-(1S,2R/1R,2S)-2-aminocyclohex-1-yl-N-(thymin-1-yl-acetyl) glycinate (10a and 10b) via enzymatic resolution of the key racemic intermediate trans-2-azido cyclohexanols 3 is reported. The crystal structures of 10 show equatorial disposition of the tertiary amide group, with the torsion angle beta in the range 60-70 degrees. The PNA oligomers incorporating these show differential effects in hybridizing with complementary DNA and RNA.     

cis-Cyclopentyl PNA (cpPNA) as constrained chiral PNA analogues: stereochemical dependence of DNA/RNA hybridization

DNA/RNA hybridization studies of PNA-T oligomers with cis-(1S,2R/1R,2S)-cyclopentyl units in the backbone show stereochemistry dependent binding with RNA/DNA discrimination.     

Expanding the repertoire of pyrrolidyl PNA analogues for DNA/RNA hybridization selectivity: aminoethylpyrrolidinone PNA (aepone-PNA)

New PNA analogues derived from aminoethylpyrrolidin-5-one backbone show stabilization of aepone-PNA:DNA hybrids and destabilization of the corresponding RNA hybrids compared to unmodified PNA.     

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.     

Development of versatile cis- and trans-dicarbon-substituted chiral cyclopropane units: synthesis of (1S,2R)- and (1R,2R)-2-aminomethyl-1-(1H-imidazol-4-yl)cyclopropanes and their enantiomers as conformationally restricted analogues of histamine

The cyclopropane ring can be used effectively in restricting the conformation of biologically active compounds to improve activity and also to investigate bioactive conformations. We designed (1S,2R)- and (1R,2R)-2-aminomethyl-1-(1H-imidazol-4-yl)cyclopropanes (1 and 2, respectively) and their enantiomers (ent-1 and ent-2) as conformationally restricted analogues of histamine. The four types of chiral cyclopropanes bearing two differentially functionalized carbon substituents in a cis or trans relationship on a cyclopropane ring, (1S,2R)-2-(tert-butyldiphenylsilyloxy)methyl-1-formylcyclopropane (7) and (1R,2R)-2-(tert-butyldiphenylsilyloxy)methyl-1-formylcyclopropane (8) and their enantiomers (ent-7 and ent-8), were developed as the key intermediates for synthesizing 1, 2, ent-1, and ent-2. The reaction between (R)-epichlorohydrin [(R)-12] and phenylsulfonylacetonitrile (13a) in the presence of NaOEt in EtOH followed by treatment with acid gave the chiral cyclopropane lactone 11a with 98% ee in 82% yield. Compound 11a was converted into both the cis- and trans-chiral cyclopropane units 7 and 8, respectively, via reductive desulfonylation with Mg/MeOH as the key step. The corresponding enantiomers, the cis-substituted ent-7 and the trans-substituted ent-8, were also prepared starting from (S)-epichlorohydrin [(S)-12]. The four conformationally restricted target histamine analogues 1, 2, ent-1, and ent-2 were successfully synthesized from 7, 8, ent-7, and ent-8, respectively. The chiral cyclopropane units 7, 8, ent-7, and ent-8 should be useful as versatile intermediates for synthesizing various compounds having an asymmetric cyclopropane structure.     

Backbone extended pyrrolidine PNA (bepPNA): a chiral PNA for selective RNA recognition

Synthesis of cationic, chiral PNA analogues with an extra atom in the backbone (bepPNA) is reported. The (2S,4S) geometry of the pyrrolidine ring, and an additional carbon atom in the backbone of homopyrimidine-bepPNAs resulted in the optimization of the inter-nucleobase distance, such that selective binding to complementary RNA over DNA was observed in the triplex mode. It was evident from circular dichroism studies that oligomers with mixed aminoethylglycyl-bep (aeg-bep) repeating units, and also bepPNA with homogeneous backbone attained structures quite different from those of aegPNA₂:RNA/DNA complexes. The bepPNA, when incorporated in a duplex forming mixed purine-pyrimidine sequence, also showed a preference for binding complementary RNA over DNA.     

Synthesis of N-propynyl analogues of peptide nucleic acid (PNA) monomers and their use in the click reaction to prepare N-functionalized PNAs

Application of the click reaction for coupling a 2-(2-aminoethoxy)ethoxy (AEE) function to thyminyl, cytosinyl and adeninyl peptide nucleic acid (PNA) monomer analogues bearing a N-propynyl group, in place of the original N-2-aminoethyl moiety, has been explored. The N-propynyl PNA analogues were prepared from glycine ethyl ester hydrochloride and the structure of the thyminyl derivative was confirmed by X-ray diffraction. These monomers were employed in click reactions with Boc-protected AEE azide to afford the corresponding triazolyl-linked PNA-AEE conjugates in yields ranging from 64 to 76%. [1,4]-Regiochemistry was verified from a NOESY correlation experiment.     

New analogues of fosfomycin—synthesis of diethyl (1R,2R)- and (1S,2R)-1,2-epoxy-3-hydroxypropylphosphonates

The trans-configured fosfomycin analogue, diethyl (1R,2R)-1,2-epoxy-3-hydroxypropylphosphonate, was synthesised via the intramolecular Williamson reaction from 3-O-protected (trityl or TBDMS) or even unprotected diethyl (1S,2R)-2,3-dihydroxy-1-mesyloxypropylphosphonate, which was obtained from the known diethyl (1S,2R)-2,3-O-cyclohexylidene-1,2,3-trihydroxypropylphosphonate. On the other hand, the cis-analogue, diethyl (1S,2R)-1,2-epoxy-3-hydroxypropylphosphonate, could only be prepared from diethyl (1R,2R)-2-hydroxy-1-mesyloxy-3-trityloxypropylphoshonate.     

An Easy Entry to (1S, 2S) and (1R, 2R)-Threo-Ifenprodil

A facile and practical synthesis of enantiomerically pure (L) or (D)-threo-Ifenprodil was accomplished from (1S, 2S)- and (1R, 2R)-threo-1-(p-nitrophenyl)-2-amino-propan-1, 3-diol via 3-phenylthio derivatives followed by Raney nickel reduction and conversion of the aromatic amine into phenol.     

(1R,2S)或(1S,2R)-1,2-二苯基-2-氨基乙醇衍生物手性配体的合成及其用于不对称催化反应

重点报道了以（１Ｒ，２Ｓ）或（１Ｓ，２Ｒ）－１，２－二苯基－２－氨基乙醇衍生物手性配体的合成及其用于不对称催化反应的研究，如去氢氨基酸的氢化、醛的乙基锌加成、酮的还原、活泼亚甲基化合物的烷基化、醛的硅腈化和瑞福马斯基反应等．研究了手性配体的结构、底物和反应条件等对上述反应的对映选择性和催化活性的影响．     

(-)-(1R,2S)-肉豆蔻木脂素的不对称合成

报道了天然产物(-)-肉豆蔻木脂素的全合成. 以香草醛为起始原料, 经Wittig反应、LiAlH₄还原和Sharplass不对称双羟化等反应构建了苏式结构的中间体; 以焦性没食子酸为原料, 经Claisen重排反应制得另一种苯丙素片段; 2个中间体通过Mitsunobu反应, 缩合并使构型翻转, 得到赤式-(-)-肉豆蔻木脂素. 为赤式8-O-4′新木脂素的合成提供了一种新方法.     

Enzymatic preparation of (1S,2R)- and (1R,2S)-stereoisomers of 2-halocycloalkanols

The stereoisomers of cis-2-halocycloalkanols were resolved by a kinetically controlled transesterification with vinyl acetate in the presence of lipases in organic media. High enantioselectivities (ee >98%) and good isolated yields were obtained for all substrates using the appropriate lipase. Burkholderia cepacia lipase was the most efficient enzyme for the resolution of these substrates. The enantiomeric purities of the compounds were defined by derivatization with Mosher’s acid and the absolute configurations were determined by chemical correlation.     

Synthesis and Crystal Structure of 5（R）-（1R,2S,5R）-Menthoxy-4（R）- N-cyclohexylaminobutyrolactone

1INTRODUCTION Substitutedγ-butyrolactones are a group of impor-tant compounds containing unique carbon skeleton of butyrolactone which is widely present in many natural products and have received considerable interest because of their biological and medicinal properties[1～4].Therefore,much attention has been paid to the new asymmetric methods for synthesi-zing these interesting compounds[5～11].The prece-ding results led us to explore the possibility of using cyclohexylamine to convert5(…     

Chimeric (aeg-pyrrolidine)PNAs: synthesis and stereo-discriminative duplex binding with DNA/RNA

The design and facile conversion of naturally occurring 4-hydroxyproline to all four diastereomers of thymine pyrrolidine PNA monomer, (2R,4S)-adenine, -guanine and -cytosine monomers and their incorporation into duplex forming PNA oligomers is reported. The interesting results of the hybridization studies with complementary DNA/RNA sequences in either parallel or antiparallel orientation reveal the stereochemistry-dependent DNA vs. RNA discriminations and parallel/antiparallel orientation selectivity.     

Synthesis and modeling study of (2S,5R,6R)- and (2S,5R,6S)-6-hydroxy- 8-(1-decynyl)-benzolactam-V8 as protein kinase C modulators

[structures: see text] Both (2S,5R,6R)- and (2S,5R,6S)-6-hydroxy-8-(1-decynyl)benzolactam-V8 were designed and synthesized as PKC modulators. Biological assays reveal the (6R)-ligand to be 20-fold more potent than its (6S)-counterpart in binding to PKC alpha.     

（2S,3R）—谷象虫聚集信息素的合成

（２Ｓ，３Ｒ）┐谷象虫聚集信息素的合成黄锦霞＊李焰马兴泉陈祖兴徐章煌（湖北大学化学系武汉４３００６２）关键词（２Ｓ，３Ｒ）－谷象虫聚集信息素，合成，不对称顺式醇醛缩合反应，Ｎ－莰烷－磺内酰胺１９９７－０７－１４收稿，１９９７－０９－２９修回湖北省自然...     

Novel open-chain and cyclic conformationally constrained (R)- and (S)-α,α-disubstituted tyrosine analogues

A series of novel open-chain and cyclic conformationally constrained (R)- and (S)-α,α-disubstituted tyrosine analogues 1a–e were synthesized in good yields and high optical purities (Schemes 1 and 2). The absolute configurations of these tyrosine analogues were unambiguously determined based on the X-ray structures of the precursor diastereoisomeric peptides of type 4 and 5 . Four of these structures are described (Figs. 1–4), showing β-turn type-I geometries for dipeptides 4a, 5b , and 4c and an extended conformation for peptide 5c (Table 3). The conversion of the free amino acids 1a–c into suitably protected building blocks 11a–d and 15d,e for peptide synthesis is discussed (Schemes 3 and 4).     

Studies towards the synthesis of (1R,2S)- and (1S,2S)-1,2-epoxy-3-hydroxypropylphosphonates and (1S,2S)- and (1R,2S)-2,3-epoxy-1-hydroxypropylphosphonates

The trans-configured fosfomycin analogue, diethyl (1S,2S)-1,2-epoxy-3-hydroxypropylphosphonate, was synthesised by the intramolecular Williamson reaction of diethyl (1S,2R)-1,3-dihydroxy-2-mesyloxypropylphosphonate. The cis-analogue was obtained as O-ethyl or O,O-diethyl (1R,2S)-1,2-epoxy-3-hydroxypropylphosphonates, when (1R,2R)-1,3-dihydroxy-2-mesyloxypropylphosphonate or its 3-O-trityl derivative were used as starting materials, respectively. The intramolecular Williamson cyclisations of diethyl (1S,2R)- and (1R,2S)-1-benzyloxy-3-hydroxy-2-mesyloxypropylphosphonates led to diethyl (1S,2S)- and (1R,2S)-2,3-epoxy-1-benzyloxypropylphosphonates, respectively, with the concomitant formation of diethyl (E)-1-benzyloxy-3-hydroxyprop-1-en-1-phosphonate. From diethyl (1S,2S)- and (1R,2S)-2,3-epoxy-1-benzyloxypropylphosphonates, enantiomerically pure diethyl (1S,2S)- and (1R,2S)-1,2-dihydroxypropylphosphonates were obtained by catalytic hydrogenation, while diethyl (1S,2S)- and (1R,2S)-3-acetamido-1,2-dihydroxypropylphosphonates were produced after epoxide ring opening with dibenzylamine, acetylation and hydrogenolysis.