One-step synthesis of aminopyrimidines from 5-Oxo-4H-benzopyrans

Unexpected Results in the Friedländer Reaction of 4-aryl-7,7-Dimethyl-5-Oxo-5,6,7,8-Tetrahydro-4H-[1]Benzopyran-3-Carbonitriles

In the Friedländer reaction of 4-aryl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4 H-[1]benzopyran-3-carbonitriles (1, 2), we have detected and isolated the unexpected imidates 5 and 6, respectively, in addition to the expected tetracyclic tacrine-like derivatives.

A Critical Evaluation of the Quality of Published 13C NMR Data in Natural Product Chemistry

Nuclear Magnetic Resonance spectroscopy contributes very efficiently to the structure elucidation process in organic chemistry. Carbon-13 NMR spectroscopy allows direct insight into the skeleton of organic compounds and therefore plays a central role in the structural assignment of natural products. Despite this important contribution, there is no established and well-accepted workflow protocol utilized during the first steps of interpreting spectroscopic data and converting them into structural fragments and then combining them, by considering the given spectroscopic constraints, into a final proposal of structure. The so-called "combinatorial explosion" in the process of structure generation allows in many cases the generation of reasonable alternatives, which are usually ignored during manual interpretation of the measured data leading ultimately to a large number of structural revisions. Furthermore, even when the determined structure is correct, problems may exist such as assignment errors, ignoring chemical shift values, or assigning lines of impurities to the compound under consideration. An extremely large heterogeneity in the presentation of carbon NMR data can be observed, but, as a result of the efficiency and precision of spectrum prediction, the published data can be analyzed in substantial detail.This contribution presents a comprehensive analysis of frequently occurring errors with respect to ¹³C NMR spectroscopic data and proposes a straightforward protocol to eliminate a high percentage of the most obvious errors. The procedure discussed can be integrated readily into the processes of submission and peer-reviewing of manuscripts.

Synthesis of Tetrahydrobenzo[b]Pyran Derivatives Catalysed by Aliquat®336 in Water Under Microwave Irradiation

A series of 4 H-5,6,7,8-tetrahydrobenzo[ b]pyran derivatives has been synthesised in excellent yield in a single pot using trioctylmethylammonium chloride (Aliquat®336) as phase-transfer catalyst in water under microwave irradiation. This method provides a clean access to the desired products. The structures of the products were confirmed by IR, 1H NMR, 13C NMR in all cases and HRMS in several cases, and supported by single crystal X-ray diffraction analysis of 2-amino-4-(3-benzyloxy-4-methoxyphenyl)-3-cyano-7,7-dimethyl-5-oxo-4 H-5,6,7,8-tetrahydrobenzo[ b]pyran and 2-amino-3-cyano-4-(3-iodo-4-hydroxy-5-methoxyphenyl)-7,7-dimethyl-5-oxo-4 H-5,6,7,8-tetrahydrobenzo[ b] pyran.

New multipotent tetracyclic tacrines with neuroprotective activity

The synthesis and the biological evaluation (neuroprotection, voltage dependent calcium channel blockade, AChE/BuChE inhibitory activity and propidium binding) of new multipotent tetracyclic tacrine analogues (5-13) are described. Compounds 7, 8 and 11 showed a significant neuroprotective effect on neuroblastoma cells subjected to Ca(2+) overload or free radical induced toxicity. These compounds are modest AChE inhibitors [the best inhibitor (11) is 50-fold less potent than tacrine], but proved to be very selective, as for most of them no BuChE inhibition was observed. In addition, the propidium displacement experiments showed that these compounds bind AChE to the peripheral anionic site (PAS) of AChE and, consequently, are potential agents that can prevent the aggregation of beta-amyloid. Overall, compound 8 is a modest and selective AChE inhibitor, but an efficient neuroprotective agent against 70mM K(+) and 60microM H(2)O(2). Based on these results, some of these molecules can be considered as lead candidates for the further development of anti-Alzheimer drugs.