A cation molecular exchanger has been developed that consists of the bipyridine and crown ether receptor subunits. It has been shown that binding of the zinc(II) cation to the bipyridine subunit induces the conformational switching of the crown ether subunits, which results in a release of the potassium cation. Two conformational states of the cation exchanger have been supported by the results from solution- and solid-state studies. It has been demonstrated that the cation exchanger is able to communicate with a cation sensor induced by a chemical stimulus.
A highly stereoselective total synthesis of polyrhacitide B is reported. Key reactions are an iodocyclization protocol developed in our group, the Maruoka asymmetric allylation, the BartlettSmith iodocarbonate cyclization, and iodolactonization.Two new aliphatic bicyclic polyketide lactones known as polyrhacitide A (1) and polyrhacitide B (2) (Figure 1) were isolated from the Chinese ant species Polyrhacis lamellidens by Jiang and Kouno in 2008. 1 These ants are widely distributed in mainland China and have been used as an effective folk medicine to treat rheumatoid arthritis and hepatitis. 2 Polyrhacitides A (1) and B (2) have syncentered 1,3-polyhydroxy units with a bicyclic lactone unit that is unusual in ants, although related compounds occur in plants of various families. 3 This unit was also found to be present as a constituent in molecules obtained from the tree extracts of Cryptocarya species. 3c The structures of polyrhacitides A (1) and B (2) were determined by exhaustive NMR investigations, whereas the absolute configurations were ascertained by applying Rychnovsky's acetonide method 4 and Mosher's MTPA ester method. 5,6 Biological evaluation of extracts of P. lamellidens demonstrated remarkable analgesic and anti-inflammatory activities, which supported the traditional use of the medicinal ants in the treatment of various diseases associated with inflammation. 7 The distinctive biological activities, fascinating structural architecture, and scarce availability of polyrhacitides have attracted our attention to develop appropriate synthetic methods for these molecules.Menz and Kirsch reported the first total synthesis of polyrhacitides A and B by using the catalytic asymmetric Overman esterification to install all the stereogenic centers. 8 In all previously reported approaches to polyrhacitides A and B, intramolecular Michael addition reaction was the only route for the synthesis of the bicyclic lactone core at the end, which restricts the generation of synthetic analogues. 9 Our efforts towards the total synthesis of polyketide natural products have led to the development of new strategies for these kinds of molecules by overcoming this constraint. Recently, we have reported a highly stereoselective synthesis of trans-2,6-disubstituted dihydropyran using molecular iodine as an inexpensive and eco-friendly Lewis acid catalyst. 10 As part of our ongoing research on iodocyclization reactions and their applications towards the assembly of complex natural products, we have reported the highly stereoselective and concise synthesis of polyrhacitides A and epi-cryptocaryolone. 11 Herein, we report the total synthesis of polyrhacitide B by a successful implementation of a previously developed strategy in our laboratory for the synthesis the trans-pyran ring. Other key steps include the Bartlett-Smith iodocarbonate cyclization reaction to construct the syn-1,3-polyol systems. Figure 1 Structures of polyrhacitides A and BIn our synthetic plan (Scheme 1), we envisaged that the bicyclic lactone could be constructe...
Highly stereoselective total syntheses of polyrhacitide A and epi-cryptocaryolone have been achieved in 11 steps with high overall yield of 24% and 28%, respectively, following a recently developed strategy for the construction of trans-2,6-disubstituted-3,4-dihydropyrans. In this report, the versatility of iodo-cyclization for the total syntheses of polyrhacitide A and epi-cryptocaryolone is demonstrated.
In ribosomopathies, perturbed expression of ribosome components leads to tissue-specific phenotypes, such as limb and craniofacial defects as well as bone marrow failure. What accounts for such tissue-selective manifestations and what role translation plays is poorly understood. Combining comprehensive mouse genetics and in vivo ribosome profiling, we observe limb patterning phenotypes in ribosomal protein (RP) haploinsufficient embryos and uncover corresponding selective translational changes of transcripts controlling limb development. Surprisingly, either loss of p53, which is activated by RP haploinsufficiency, or augmented protein synthesis rescues these phenotypes. These findings are reconciled by the unexpected identification of p53 as a master regulator of protein synthesis, which specifically induces 4E-BP1 expression. 4E-BP1, a key regulator of gene expression at the translation level, facilitates selective changes in the translatome and thereby explains, at least in part, how RP haploinsufficiency may elicit specificity to gene regulation. These results provide an integrative model to explain how a tissue-specific phenotype may emerge from a mutation in a ribosome component. ONE SENTENCE SUMMARYA p53-4E-BP1 axis imparts translational remodeling associated with selective developmental phenotypes in an in vivo ribosomopathy model. 2
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