Facile synthesis of 1-alkoxy-1H-benzo- and 7-azabenzotriazoles from peptide coupling agents, mechanistic studies, and synthetic applications

Base Modifications of Nucleosides via the Use of Peptide-Coupling Agents, and Beyond

Several naturally occurring purine and pyrimidine nucleosides contain an amide linkage as part of the heterocyclic aglycone. Enolization of the amide and conversion to leaving groups at the amide carbon atom permits base modification by addition-elimination types of processes. Although a number of methods have been developed over the years for accomplishing such conversions, the present Personal Account describes efforts from the Lakshman laboratories. Facile activation of the amido groups in nucleobases can be achieved with peptide-coupling agents. Subsequent reaction with nucleophiles then accomplishes the base modifications. In many cases, the activation and displacement steps can be done as two-step, one-pot processes, whereas in other cases, discrete storable activated nucleosides can be isolated for subsequent displacement reactions. Using such an approach a wide range of nucleoside base modifications is readily achievable. In many instances, mechanistic investigations have been conducted so as to understand the activation process.

Modification of Sesquiterpene Lactones—Dehydrocostus Lactone and Alantolactone—by Click Chemistry Method. Cytotoxic Activity of the Obtained Conjugates

Abstract

A method for modifying sesquiterpene lactones using the click chemistry methodology has been developed. A series of conjugates of alantolactone and dehydrocostus lactone with alkoxy substituted benzylazides was obtained and their cytotoxic profile with respect to tumor cells of the A549, SH-SY5Y, Hep-2 and HeLa lines was evaluated. It has been shown that derivatives containing dehydrocostus lactone motif in their structure exhibit the highest cytotoxic activity.

Coetaneous catalytic kinetic resolution of alkynes and azides through asymmetric triazole formation

A non-enzymatic simultaneous (coined coetaneous) kinetic resolution of a racemic alkyne and racemic azide, utilising an asymmetric CuAAC reaction is reported. The use of a CuCl (R,R)-Ph-Pybox catalyst system effects a simultaneous kinetic resolution of two racemic starting materials to give one major triazolic diastereoisomer in the ratio 74:12:4:10 (dr 84:16, 90% ee maj). The corresponding control reaction using an achiral copper catalyst gives the four possible diastereoisomers in a 23:27:23:27 ratio, demonstrating minimal inherent substrate control.

Facile Modifications at the C4 Position of Pyrimidine Nucleosides via In Situ Amide Activation with 1H-Benzotriazol-1-yloxy-tris(dimethyl-amino)phosphonium Hexafluorophosphate

Two approaches for C4 modifications of silyl-protected thymidine, 2'-deoxyuridine, and 3'-azido-2',3'-dideoxythymidine (AZT) are described. In both, nucleoside amide activation with 1H-benzotriazol-1-yloxy-tris(dimethylamino)phosphonium hexafluorophosphate (BOP) and DBU yields O⁴ -(benzotriazol-1-yl) derivatives. These in situ-formed intermediates are reacted with various nucleophiles, resulting in C4 modifications. In the two-step, one-pot approach, the O⁴ -(benzotriazol-1-yl) nucleoside intermediates are initially produced by reactions of the nucleosides with BOP and DBU in THF. This step is fast and typically complete within 30 min. Subsequently, the O⁴ -(benzotriazol-1-yl) derivatives are reacted with nucleophiles, such as aliphatic and aromatic amines, thiols, and alcohols, under appropriate conditions. Workup, isolation, and purification lead to the desired C4-modified pyrimidine nucleosides in good to excellent yields. In the one-step approach, the nucleosides are reacted with BOP and DBU, in the presence of the nucleophile (only aliphatic and aromatic amines, and thiols have been tested). Where comparisons are possible, the one-step approach is generally superior. © 2019 by John Wiley & Sons, Inc.

Facile functionalization at the C4 position of pyrimidine nucleosides via amide group activation with (benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate (BOP) and biological evaluations of the products

Reactions of O-t-butyldimethylsilyl-protected thymidine, 2'-deoxyuridine, and 3'-azidothymidine (AZT) with (benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate (BOP) leads to activation of the C4 amide carbonyl by formation of putative O4-(benzotriazol-1-yl) derivatives. Subsequent substitution with alkyl and aryl amines, thiols, and alcohols leads to facile functionalization at this position. Reactions with amines and thiols were conducted either as a two-step, one-pot transformation, or as a one-step conversion. Reactions with alcohols were conducted as two-step, one-pot transformations. In the course of these investigations, the formation of 1-(4-pyrimidinyl)-1H-benzotriazole-3-oxide derivatives from the pyrimidine nucleosides was identified. However, these too underwent conversion to the desired products. Products obtained from AZT were converted to the 3'-amino derivatives by catalytic reduction. All products were assayed for their abilities to inhibit cancer cell proliferation and for antiviral activities. Many were seen to be active against HIV-1 and HIV-2, and one was active against herpes simplex virus-1 (HSV-1).

Diarylmethanes through an Unprecedented Palladium-Catalyzed C-C Cross-Coupling of 1-(Aryl)methoxy-1 H-Benzotriazoles with Arylboronic Acids

1-(Aryl)methoxy-1H-benzotriazoles (ArCH2OBt) are bench-stable reagents that are prepared readily from 1H-benzotriazol-1-yl-4-methylbenzenesulfonate (BtOTs) and benzylic alcohols. These compounds, which contain a N-O-C bond, undergo cross-coupling with arylboronic acids by C-O bond scission with catalysts that comprise Pd(OAc)2 and biarylphosphine ligands. Such reactivity of ArCH2OBt derivatives, leading to diarylmethanes, has not been described previously and constitutes a new activation of benzylic alcohols. With regard to the various ligands-metal complexes that support catalytic activity, it appears that those with smaller "percent buried volumes" (%Vbur) provide better outcomes. This factor has been evaluated in the initial optimization studies and in further reactions with difficult coupling partners. Ligand electronics of the biaryl moiety seem to play a lesser role in this type of reaction. The bis-coordinating bis[(2-diphenylphosphino)phenyl]ether appears to be suitable to improve the yields of low-yielding reactions.