ABSTRACT
To explore the reaction universality of bridge nitration, the mononitration of different p-tert-butylcalix[4]arene derivatives was executed with tert-butyl nitrite as a nitration reagent. The effects of calix[4]arene conformations, substituents on the lower rim, and reaction conditions on bridge mononitration are systematically studied. The bridge nitration of p-tert-butylcalix[4]arene derivatives in 1,3-alternate, 1,2-alternate, and partial cone conformations can be smoothly executed while that of p-tert-butylcalix[4]arene derivatives strictly regulated in a cone conformation cannot. The nitration product complexity shows a positive correlation with the bridge-hydrogen types, and the optimal bridge-mononitrated substrate is calix[4]arene with only one bridge-hydrogen type. The electron-withdrawing substituent on the lower rim is apparently beneficial for the bridge mononitration. As a result, a variety of bridging chiral p-tert-butylcalix[4]arenes with a mononitro bridge substituent have been successfully synthesized. The highest bridge-mononitrated yield can reach 27% from 1,3-alternate p-tert-butylcalix[4]arene biscrown-5 under optimal reaction conditions.
ABSTRACT
In order to prepare bridging chiral p-tert-butylcalix[4]crown-5 with a mononitro bridge substituent in a 1,3-alternate conformation, a mononitration method of calix[4]arene bridging methylene has been first developed with tert-butyl nitrite as a nitration reagent. The effects of solvent, reaction temperature, reaction time, and nitration reagent dosage on bridge mononitration have been deeply explored to obtain an optimal nitration condition. The facile nitration presents a new key for calix[4]arene bridge derivatization. After further modification and diastereoisomeric resolution, a pair of bridging chiral p-tert-butylcalix[4]arenes with a monoamino bridge substituent were produced from the bridge-mono-nitrated calix[4]arene. Their preliminary catalysis results in the Henry reaction show good catalytic activities (up to 95% yield) and still low but obviously enhanced enantioselectivities (up to 22.3% ee from 7a, 6% ee from 1), which confirms that the structural transformation indeed improves asymmetric catalysis performances of bridging chiral calix[4]crown-5 amines in a 1,3-alternate conformation.
ABSTRACT
BACKGROUND & OBJECTIVE: Multiple steps and gene expression changes were involved in the development and progression of nasopharyngeal carcinoma (NPC), but the molecular mechanism is not understanding clearly. This study was designed to investigate the profiling of differently expressed genes in nasopharyngeal carcinoma compared with noncancerous nasopharynx tissues to explore the feature of gene expression in NPC and identify new candidate genes related to the development and progression of NPC. METHODS: Differently expressed genes of NPC in 21 cases, which were divided into three pools, were investigated by using high density cDNA microarray representing 18,000 cDNA clones. The alterations in gene expression levels were confirmed by reverse-transcription PCR in 2 randomly selected genes. RESULTS: A total of 317 genes were identified to be differently expressed in NPC of three pools as compared with noncancerous controls. Among the 317 genes, 23 genes were found to be consistent in at least two NPC sample pools, including 16 up-regulated genes and 7 down-regulated genes. Six genes were found to be consistent in all the three NPC sample pools. The 6 genes include 2 up-regulated unknown genes, 3 up-regulated unknown genes and 1 down-regulated unknown gene. CONCLUSION: The present study represents a global view of gene expression of NPC and provides important clues for further study of NPC related genes.
