The conditions the group eventually found gave the desired compound in just 14% yield (after treatment with methanol to give a more stable product). Next, a suitable cuprate was added to the enal, and the resulting enolate was trapped as the TMS enol ether. Ozonolysis of this enol ether, followed by reductive work-up with sodium borohydride successfully set the compound’s final stereogenic centre, with hydride unsurprisingly being delivered from the less hindered convex top face. All that remained was to introduce the remaining side chain, and this was easily carried out using some well established Wittig chemistry to give the product in just six steps from succinaldehyde (which is made in one step by hydrolysis of 2,5-dimethoxytetrahydrofuran).
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“The reaction was repeated using the crude material from the conjugate addition/trapping experiment which had been carried out on 4 g of enal. In this case, Sudan Red 7B (7.5 mg) was added as a rough indicator of the end of the ozonolysis and 240 ml of CH2Cl2/MeOH (3:1) used. The purple colour of the reaction mixture faded slightly as most of the silyl enol ether had reacted. At that point, careful monitoring of the reaction by TLC was carried out.”
The title of the paper is “Stereocontrolled organocatalytic synthesis of prostaglandin PGF2a in seven steps” but gave “the product in just six steps”?
In the last step the phosphonium is one carbon short, and how can a 47% yield give 1.9 g of a lower-MW (lost the heavy TBS) product starting from only 1.4 g?
A couple of the sentences in the optimization paragraph are backwards. Normally you’s expect the 2nd aldol to be in favor of the intramolecular reaction and the second catalyst could not be present at the same time.
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Although miRNAs were only discovered 20 years ago,their molecular mechanisms of action involving the repression oftarget gene expression have been elucidated. Moreover, evidenceindicates that miRNAs are associated with the development of anumber of human diseases. The process from the time of discovery ofan miRNA to the development of clinical therapeutic drug targets israpidly approaching. miR-34a has been shown to suppress thedevelopment of prostate and lung cancer (,), and the use of a miR-34a mimic iscurrently in the developmental stage for cancer therapy (, The Therapeutic Potential ofmicroRNAs). Another miRNA, miR-208, which is involved in promotingchronic heart failure (), isalso undergoing investigation in preclinical trials (, The Therapeutic Potential ofmicroRNAs). Its antagonist is expected to be used in the therapy ofheart disease. miR-122 has been shown to be associated withhepatitis C virus infection (), and its antagonist, miravirsen, hasundergone phase II clinical trials for the therapy of patients withhepatitis C virus ().Miravirsen may be the first miRNA-related drug for clinicaltherapy. Taken together, the mimics or antagonists of miRNAs areexpected to be widely used in clinical therapy.
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As small non-coding RNAs, miRNAs play a pivotal rolein post-transcriptional regulation. miRNAs can bind to and promotethe deadenylation and degradation of target mRNAs (,). Translational repression is anotherimportant function of miRNAs. It can directly bind to the 3′-UTR oftarget mRNAs and inhibit the translational initiation (). Studies have demonstrated thatmiRNAs are involved in the regulation of multiple insulinresistance-induced diseases (). In T2D, miR-144 has been shown to promote insulinresistance by directly targeting mRNA (). The suppression of IRS1 mediated bymiR-126 has also been shown to result in mitochondrial dysfunctionand insulin resistance (). Thesitmulation of Akt activation by insulin is critical forglycometabolism, and the obesity-induced miR-143 overexpression hasbeen shown to lead to hyperglycemia by inactivating the Aktsignaling pathway (). A studyusing let-7 family transgenic mice demonstrated that let-7overexpression may contribute to the development of T2D (). Protein tyrosine phosphatase 1B(PTP1B) impairs the insulin signaling pathway through thedephosphorylation of IR at tyrosine residues. The 3′-UTR of mRNA is the target of miR-122, and decreased miR-122expression has been shown to result in hepatic insulin resistance(). In mouse models ofobesity, miR-103/107 is upregulated. The blockage of miR-103/107has been shown to promote insulin sensitivity by elevatingcaveolin-1-mediated IR activation (). Phosphatase and tensin homologdeleted on chromosome 10 (PTEN), the direct target of miR-21(), is the key phosphotase ofAkt which can negatively regulate the Akt signaling pathway. Ininsulin-resistant adipocytes, the suppressed expression of miR-21and impaired Akt signaling pathway has been observed (). The transport of glucose is alsoregulated by miRNAs, and the transmembrane protein GLUTs play anessential role in glucose transport. Elevated miR-133 levels havebeen shown to reduce the insulin-stimulated glucose uptake bydownregulating GLUT4 expression (). In cardiomyocytes, miR-223 has beenshown to promote GLUT4 expression and increase glucose uptake(). Insulin resistance is theintrinsic complication of polycystic ovary syndrome (PCOS), andoverexpressed miR-93 in patients with PCOS binds to the 3′-UTR of mRNA and reduces its protein translation (). Microarray analysis has furtherindicated that the expression of several miRNAs is alteredfollowing burn injury. In comparison with normal skin tissue, atotal of 32 upregluated and 34 downregulated miRNAs were identifiedin the skin tissue of patients who sustained burn injuries(). The expression levels ofmiR-144 in the skin tissue of the burned patients, which candirectly target the 3′-UTR of mRNA (), were 16-fold higher than those innormal skin tissue (). Thissuggests that miRNAs, such as miR-144, play an essential role inpromoting burn-induced insulin resistance by suppressing theactivation of the IR/IRS signaling pathway.