A highly regio- and diastereoselective TiCl4-mediated vinylogous Mukaiyama aldol reaction using the chiral vinylketene silyl N,O-acetal has been developed. The present vinylogous Mukaiyama aldol reaction provides a unique and effective means of controlling remote asymmetric induction. The methyl group at the alpha-position is important in achieving a high level of stereoselectivity. From a synthetic point of view, this methodology can provide a one-step construction of delta-hydroxy-alpha,gamma-dimethyl-alpha,beta-unsaturated carbonyl unit that is seen in many natural polyketide products.

Peroxynitrite (ONOO), is a potent oxidant that can cause severe cell damage.1) Specifically, peroxynitrite promotes the oxidation of biomolecules such as lipids, proteins and nucleic acids, [2][3][4] as well as the nitration of tyrosine residues in proteins. 5,6) Furthermore, it has been suggested that peroxynitrite formation plays a role in the pathogenesis of neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. [7][8][9] Neoechinulin A (1), an isoprenyl indole alkaloid, can protect neuronal PC12 cells from ONOO Ϫ -induced death. [10][11][12] We have previously shown that the biological effects, rather than scavenging activity against ONOO Ϫ , are likely to play a role in the cytoprotective action of neoechinulin A.12) However, the precise molecular mechanism remains elusive. To investigate the potential mechanism of action, we have designed and prepared a series of neoechinulin A analogues (2-6). We then examined the structure-activity relationships of these analogues in terms of their anti-nitration and anti-oxidant activities as well as their cytoprotective activity against ONOO Ϫ derived from SIN-1 (3-(4-morpholinyl)sydnonimine hydrochloride) using PC12 cells (Fig. 1). The results showed that: 1) the presence of the C-8/C-9 double bond is indispensable for anti-nitration and anti-oxidant activities as well as cytoprotective activity of neoechinulin A against ONOO Ϫ toxicity; 2) in conjunction with the C-8/C-9 double bond, the presence of an intact diketopiperazine moiety is essential for the anti-nitration activity but not for antioxidant or cytoprotective activity. Results and DiscussionCompound 2 was synthesized from 2-tert-butyl-1H-indole (7) 13) (Chart 1). Methoxy methyl (MOM) protection of 7, followed by the Vilsmeier reaction, gave aldehyde 9. A coupling reaction of the aldehyde 9 with diketopiperazine 10 using tBuOK in DMF afforded 11.14) Subsequent deprotection of protective groups provided the desired product 2. 15)Compound 3 was prepared by coupling of aldehyde 12 with N-Boc-Gly-OEt, followed by treatment of the resulting We synthesized a series of neoechinulin A derivatives and examined the structure-activity relationships in terms of their anti-nitration and anti-oxidant activities as well as their cytoprotective activity against peroxynitrite from SIN-1 (3-(4-morpholinyl)sydnonimine hydrochloride) using PC12 cells. Our results showed that the C-8/C-9 double bond, which constitutes a conjugate system with indole and diketopiperazine moieties of neoechinulin A is essential for anti-nitration and anti-oxidant activities as well as protection against SIN-1 cytotoxicity. The presence of an intact diketopiperazine moiety is an additional requirement for anti-nitration activity but not for the cytoprotective action. Our results suggest that the antioxidant activity or electrophilic nature of the C-8 carbon, both of which are afforded by the C-8/C-9 double bond, may play a role in the cytoprotective properties of this alkaloid.

Neoechinulin A, an alkaloid from Eurotium rubrum Hiji025, protected neuronal PC12 cells against cell death induced by peroxynitrite derived from SIN-1 (3-(4-morpholinyl)sydnonimine hydrochloride). In this study, we investigated the structure-activity relationships of neoechinulin A and a set of its analogues by using assays to measure anti-nitration and antioxidant activities and cytoprotection against SIN-1-induced PC12 cell death. The presence of the diketopiperazine ring was essential for both the antioxidant and anti-nitration activities of neoechinulin A derivatives. Nevertheless, a derivative lacking the diketopiperazine ring could still protect PC12 cells against SIN-1 cytotoxicity. An acyclic analogue completely lost the cytoprotective effect while retaining its antioxidant/anti-nitration activities. Pre-incubation of the cells with neoechinulin A for at least 12 hours was essential for the cells to gain SIN-1 resistance. These results suggest that neoechinulin A endows the cells with cytoprotection through a biological effect different from the apparent antioxidant/anti-nitration activities.

Lolitrems are tremorgenic indole diterpenes that exhibit a unique 5/6 bicyclic system of the indole moiety. Although genetic analysis has indicated that the prenyltransferase LtmE and the cytochrome P450 LtmJ are involved in the construction of this unique structure, the detailed mechanism remains to be elucidated. Herein, we report the reconstitution of the biosynthetic pathway for lolitrems employing a recently established genome‐editing technique for the expression host Aspergillus oryzae. Heterologous expression and bioconversion of the various intermediates revealed that LtmJ catalyzes multistep oxidation to furnish the lolitrem core. We also isolated the key reaction intermediate with an epoxyalcohol moiety. This observation allowed us to establish the mechanism of radical‐induced cyclization, which was firmly supported by density functional theory calculations and a model experiment with a synthetic analogue.

[reaction: see text] The first enantioselective total synthesis of convolutamydines B and E has been achieved using our vinylogous Mukaiyama aldol reaction. The synthesis features highly diastereoselective vinylogous Mukaiyama aldol reaction with isatin instead of aldehydes to construct a chiral center of convolutamydines. Additionally, the absolute configuration of natural convolutamydine B has been determined as R by its CD spectrum.