Unique Substitution Pattern Research Articles

Regioselective alkylation of a methylene group via meta-bridging of calix[4]arenes.

The meta-iodo derivative, fixed in the cone conformation, enables the gram-scale preparation of a meta-bridged calix[4]arene. This intermediate, possessing a fluorene moiety within the macrocyclic skeleton, can be regioselectively alkylated on the corresponding methylene bridge to form a unique substitution pattern in classical calixarene chemistry.

ChemInform Abstract: Alkoxyallenes as Building Blocks for Organic Synthesis

AbstractReview: 55 refs.

Orthogonal Functionalization of Cyclopenta[hi]aceanthrylenes

A synthetic strategy to prepare 2,7- or 4,9-functionalized cyclopenta[hi]aceanthrylenes that are capable of Suzuki cross-coupling reactions is demonstrated. This method has been utilized to create a series of thiophene derivatized compounds that were subsequently used to investigate the role of substitution pattern on the photophysical and electronic properties of cyclopenta[hi]aceanthrylenes. The orthogonal functionalization provides access to unique substitution patterns (e.g., cruciform-like architectures) and materials with small optical band gaps (1.22-1.97 eV).

Efficient Synthesis of Quinoxaline Derivatives by Selective Modification of 3‐Chloro‐6‐fluoroquinoxalin‐2(1H)‐one 4‐Oxide

AbstractThe readily available and polyfunctionalized 3‐chloro‐6‐fluoroquinoxalin‐2(1H)‐one 4‐oxide, derived from the efficient one‐step annulation reaction of 1,1,2‐trichloro‐2‐nitroethene with 4‐fluoroaniline, was selectively modified at the chloronitrone and the amide units, leading to more than 30 new quinoxaline derivatives with a unique substitution pattern in good to excellent yields. In addition, the electronic properties of the versatile starting compound were computed by means of density functional theory, which gave a reasonable explanation for its unique reactivity. The antimalarial activity of all hitherto unknown compounds has been investigated.

Meta-arylation of calixarenes using organomercurial chemistry

A direct mercuration reaction combined with a subsequent Pd-catalyzed arylation was used to introduce the aryl moiety into the meta position of the calix[4]arene skeleton. The application of organomercurial intermediates thus allows the straightforward formation of meta-aryl-substituted derivatives representing a unique substitution pattern in calixarene chemistry.

N-heterocyclic carbene catalysed homoenolate addition to 3-methyl-4-nitro-5-styrylisoxazoles

We describe the development of an N-heterocyclic carbene catalysed homoenolate addition to 4-nitro-5-styrylisoxazoles to give substituted cyclopentanones with a unique substitution pattern and as single diastereoisomers. The synthetic utility of the cyclopentanones obtained was briefly explored through their conversion into α-fluorinated diketones and keto acids.

Meta Nitration of Thiacalixarenes

Nitration of thiacalix[4]arene, immobilized in the 1,3-alternate conformation, leads regioselectively to meta-substituted products. Depending on the reaction conditions, mono- and dinitro-derivatives can be isolated in acceptable yields. This unique substitution pattern is inaccessible in classical calixarene chemistry, and yields inherently chiral compounds, which makes thiacalixarenes very attractive as building blocks or molecular scaffolds.

Novel CGRP receptor antagonists from central amide replacements causing a reversal of preferred chirality

A previously utilized quinoline-for-N-phenylamide replacement strategy was employed against a central amide in a novel class of CGRP receptor antagonists. A unique and unexpected substitution pattern was ultimately required to maintain reasonable affinity for the CGRP receptor, while at the same time predicting acceptable heterocycle positioning for related analogs. Subsequently, specific quinoline and naphthyridine compounds were prepared which supported these structural predictions by displaying CGRP binding affinities in the 0.037–0.15nM range.

Uncommon Regioselectivity in Thiacalix[4]arene Formylation

To reveal the alternative ways for upper-rim thiacalixarene derivatization, the formylation reactions (Gross and/or Duff conditions) of the corresponding tetrapropoxythiacalix[4]arene immobilized in the 1,3-alternate conformation were systematically studied. Surprisingly, albeit using an excess of the formylation agent, only two formyl groups were introduced exclusively into the meta positions of thiacalixarene skeleton. Unexpected regioselectivity of these reactions opens the door for a unique substitution pattern in thiacalixarene chemistry. The formation of meta-substituted aldehydes is another illustration showing remarkably different reactivity of the thiacalix[4]arene system compared with that of a classical calyx[4]arene analogue.

Integrative taxonomy identifies new (and old) species in the Lasioglossum (Dialictus) tegulare (Robertson) species group (Hymenoptera, Halictidae)

An integrative taxonomic approach that utilizes the DNA barcode region of cytochrome c oxidase subunit 1 in conjunction with traditional morphological approaches identifies five distinct species previously recognized as Lasioglossum (Dialictus) tegulare (Robertson). Differences in DNA sequences and congruent, albeit minor, morphological variation support separation of L. tegulare into five species. Unique nucleotide substitution patterns for each species allows for character-based diagnostics using DNA barcodes. The names L. ellisiae (Sandhouse) and L. lepidii (Graenicher) are removed from synonymy. Two new species, L. puteulanum Gibbs sp. n. and L. carlinvillense Gibbs sp. n., are described. A key is provided, which permits the identification of both males and females. The utility of the DNA barcode region as part of an integrative taxonomic framework is discussed.

Amygdaloidins A—L, Twelve New 13 α‐OH Jatrophane Diterpenes from Euphorbia amygdaloides L.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Amygdaloidins A–L, twelve new 13 α-OH jatrophane diterpenes from Euphorbia amygdaloides L.

Twelve new diterpenes, named amygdaloidins A–L ( 1– 12 ), possessing a unique substitution pattern of the jatrophane skeleton, have been isolated from the wood spurge, Euphorbia amygdaloides L. (Euphorbiaceae). The chemical structures of amygdaloidins A–L have been established through a combination of extensive nuclear magnetic resonance and mass spectrometry methods. To deeper investigate the conformations adopted by such compounds in solution, we have carried out a molecular mechanic and dynamics calculation on amygdaloidin A and on the previously isolated euphodendroidin I. The data obtained gave further information on the endo- and exo-type conformations, the two main orientations of the jatrophane diterpenes.

Six new isoflavones and a 5-deoxyflavonol glycoside from the leaves of Ateleiaherbert-smithii.

Six new isoflavones, 5-methoxy-6,7:3',4'-bis(methylenedioxy)isoflavone (1), 3'-methoxy-6,7:4',5'-bis(methylenedioxy)isoflavone (2), 5,2'-dimethoxy-6,7:4',5'-bis(methylenedioxy)isoflavone (3), 5,3'-dimethoxy-6,7:4',5'-bis(methylenedioxy)isoflavone (4), 5-hydroxy-7,3',4'-trimethoxyisoflavone (5), and 5,6,7,3',4'-pentamethoxyisoflavone (6), were obtained from diethyl ether extracts of the leaves of Ateleia herbert-smithii together with 11 known isoflavones and two chalcones. Four of the isoflavones (1-4) are characterized by a unique bis-methylenedioxyl substitution pattern. A new flavonol glycoside, 5-deoxyisorhamnetin 3-O-alpha-l-rhamnopyranosyl(1' " --> 6' ')-beta-d-glucopyranoside (20), and three known flavonol 3-O-glycosides were obtained from aqueous methanol extracts of leaves of the same species. Spectroscopic methods were used to determine the structures of the compounds. The significance of their occurrence in A. herbert-smithii is discussed from both biosynthetic and taxonomic viewpoints.

4,5-Diaryloxazole inhibitors of cyclooxygenase-2 (COX-2).

A series of methysulfonyl or sulfonamido substituted 4,5-diaryloxazole were prepared and evaluated for their ability to inhibit the inducible form of cyclooxygenase (COX-2) in vitro and in vivo. Several unique substitution patterns were identified that led to potent and selective inhibitors of COX-2. In general, 2-trifluoromethly-4,5-diaryloxazoles substituted with a methylsulfonyl or sulfonamido group were particularly potent inhibitors. One of the more potent compounds with a selectivity for COX-2 of about 800 fold was 4b (SC-299). SC-299, a highly fluorescent molecule, may be useful for spectroscopic studies on preferential inhibitor binding to COX-2.

Poly(2-Butyne-1,4-Diyl)S as Precursors to Novel Substituted Polyacetylenes

AbstractThermally-induced polymerization of 1,4-diphenyl-1,2,3-butatriene affords poly(1,4-diphenyl- 2-butyne-1,4-diyl) as a soluble high molecular weight material. Structure is characterized by 13C and vibrational spectroscopy. When treated with base, this material rearranges to a soluble red poly(acetylene) with a unique substitution pattern.