JACS: Nuno maulide team 10 steps to complete the synthesis of macrocyclic immunosuppressant fr252921 and its analogues

Immunosuppressive drugs have been widely used in the treatment of allograft rejection and autoimmune diseases However, most immunosuppressants have serious side effects and limitations Therefore, in order to improve the safety and effectiveness of immunosuppressive therapy, it is of great significance to find new immunosuppressants with novel and unique mode of action (MOA) In 2003, in the process of studying new immunosuppressants acting on antigen-presenting cells (APCs), Fujisawa researchers isolated three new compounds from the culture medium of Pseudomonas fluorescens No 408813: fr252921, fr252922 and fr256523 (hereinafter referred to as "fr molecule", figure 1c) From the structural point of view, these molecules all have a unique 19 membered (E, e, e) - trienediolactam lactone core, which is different only in the polyene side chain Compared with the clinical drugs CSA and FK506, FR inhibited the proliferation of mouse spleen cells stimulated by LPS and anti-CD3 monoclonal antibody, and IC 50 was as low as 2.9 ng / ml and 3.9 ng / ml, respectively Further study on fr252921 showed that it could inhibit the production of IL-2 and IL-12, while FK506 and CSA only inhibited the production of IL-2 These preliminary biological studies clearly show that FR may have different action modes from the known immunosuppressant FK506 Therefore, since they were separated, FR molecules have attracted great attention in the synthesis field Although Falck and cossy team have successively realized the total synthesis of fr252921, the E / Z isomerization of C2-C3 can not be avoided (Figure 1a) Recently, Professor Nuno maulide of the University of Vienna, Austria, has overcome the above problems They reported the first case of domino Suzuki macrocyclization / 4 π - electrocyclization ring opening reaction, and applied it to the synthesis of complex molecules, thus realizing the simple and efficient total synthesis of FR molecule and its analogues in only 10 steps Relevant research results were published in J am Chem SOC (DOI: 10.1021 / JACS 9b07185) (source: J am Chem SOC.) in other studies, the author unexpectedly found that Suzuki miyaara cross coupling of vinylborate 3 and CIS chlorobutene 4, which was reversed three dimensionally, could yield (E, e, e) - triaenoate 6 in 82% yield, rather than the expected cyclization product The reaction undergoes the spontaneous cyclization and ring opening process of trans cyclobutylene 5 (Figure 1b) Inspired by this, the authors hope to use this series reaction to complete the total synthesis of FR molecule As shown in Figure 1C, using the above-mentioned domino reaction, the fr molecule can be cut into acyclic precursors and decomposed into four relatively small fragments Firstly, the fragment of boron amine 11 (Figure 2a) was synthesized The N-Boc protected amines 9 were obtained by the rearrangement of 4-pentynoic acid 8 in TERT butanol by Curtius It was then protected by zirconium promoted E-selective hydroboration and de BOC to obtain salt 11 Then, the author developed a simple and efficient four-step synthesis route (Figure 2b) of chiral γ - amino acid fragment 16 C12 methyl (D.R = 18:1) was prepared by chloro substitution and FRA ́ ter Seebach alkylation of the commercially available enantiopure ester 12 with sodium azide, and then compound 14 was protected by silane and hydrolyzed by ester to yield 16% in gram scale with a total yield of 54% Fragments 11 and 16 were coupled and reduced to azide functional group, and the key intermediate 21 was obtained at the scale of > 3.5G Under the promotion of DMAP, 21 and 29a were directly coupled to obtain 30A Then, the free alcohol is esterified with CIS chlorocyclobutanenoic acid 7 to obtain ester 31 After extensive optimization of conditions, the author found that the combination of ghosez reagent and pyridine can selectively obtain cis-31 of CIS chlorocyclobutene ester, with a yield of 79% and a cis / inverse ratio of 8.8:1 Then, the process of domino cyclization / 4 π - electrocyclization of cis-31a is investigated After a large number of screening conditions, the author found that in the presence of PD (PPH 3) 4 and CS 2CO 3, macrocyclization can be carried out selectively, and macrolide 32A containing (E, e, e) - triene was successfully obtained with a yield of 74% Finally, the author deprotected 32A with TBAF at 0 ℃, and obtained fr252921 with a yield of 90% (Figure 2C) (source: J am Chem SOC.) the author also completed the first full synthesis of fr252922 and fr256523 through a similar synthesis path, and extended to the synthesis of eleven unnatural analogues (Figure 3) The activity of the synthesized molecule was tested in the proliferation test of EL4 All of the three natural products showed effective proliferation inhibition, and the IC50 value was lower than 1 μ M The activity test results of the molecules with other side chains showed that FR5 containing CF 3 substituents was the most effective inhibitor, with IC 50 of 83 nm, more than three times of fr252921 (source: J am Chem SOC.) in a word, the author has realized the synthesis of natural macrocyclic products fr252921, fr252922 and fr256523 with immunosuppressive activity by using unique domino Suzuki macrocyclization / 4 π - electrocyclization ring opening reaction The highlights of this route include the short and efficient synthesis of chiral amino acid 16 and the mild stereoselective esterification of CIS chlorocyclobutene promoted by ghosez reagent Based on the short 10 step route, 14 compounds were synthesized and tested for anti EL4 cell proliferation, which established a clear structure-activity relationship for these compounds and identified a more effective analogue FR5.