Design And Synthesis Of Novel Cholesterol Absorption Inhibitors

This dissertation is divided into four chapters. First, the importance of research and development of cholesterol absorption inhibitor, the development and mechanism of ezetimibe, as well as analogs of ezetimibe, were summarized to achieve full understanding of ezetimibe as a cholesterol absorption inhibitor. Then, based on the anti-hyper-cholesterolemia activity of re-organized analogs of ezetimibe and the merger of ezetimibe and statin, with retention of the important structural fragments of ezetimibe, novle scaffold analogs of ezetimibe were designed and synthesized, and the activities of some compouds to inhibit cholesterol absorption were studied. These novel backbone analogs of ezetimibe had the potential cholesterol absorption inhibition activity.In chapter one, the background of cholesterol absorption inhibitor ezetimibe was summarized. Atherosclerotic coronary heart disease (CHD) is always a major concern in healthcare due to its high morbidity and mortality. The cholesterol absorption inhibitor ezetimibe inhibits the absorption of dietary or recycled cholesterol in the intestine and can be used either alone or in combination with a statin. The discovery of ezetimibe originated from a project for novel acylcoenzyme cholesterol acyltransferase (ACAT) inhibitors. A series of conformationally constrained azetidinone analogs were prepared to profile their potencies in vitro and in vivo. The subsequent extraordinarily challenging medicinal chemistry effort led to the discovery of SCH48461, the prototype azetidinone cholesterol absorption inhibitor. By pharmacokinetics study of SCH48461 and structural improvement of active metabolite, more active inhibitor ezetimibe was found. In the target and mechanistic study of ezetimibe, NPC1L1 was determined as the target of ezetimibe through the use of proteomics method, ezetimibe blocks the sterol-induced internaliztion of NPC1L1 to achieve the activity of cholesterol absorption inhibition.Previous work on novel cholesterol absorption inhibitors in Bai Lab was also summerized. With the maximum retention of the functional groups that exist in ezetimibe, four individual isomers of backbone re-organized ezetimibe analogs were designed and synthesized. Their effects on the cholesterol levels in rat serum were evaluated by a high-cholesterol and high-fat diet feeding experiment. All the new analogs showed significant effect in lowering the levels of total cholesterol in serum. A potential dual inhibitor for exogenous absorption and endogenic synthesis of cholesterol was designed based on conjugation of theβ-lactam pharmacophore of ezetimibe and theδ-lactone pharmacophore of statins, the merger was found to lower total glucose (TG) level in rat serum via a high-cholesterol and high-fat feeding experiment. As the previous work suggests, the design of novel cholesterol absorption inhibitor will follow the methodology that the active functional side chains are rearranged on novel scaffold.In Chapter two, with retention of important functional groups in ezetimibe and the core of re-organized backbone analogs was replaced by spiro-β-lactam, ezetimibe analogs 2-(3-(4-fluorophenyl)-3-hydroxypropyl)-3-(4-hydroxyphenyl)-2-azaspiro[3.5] nonane-1-one and 2-(3-(4-fluorophenyl)-3-hydroxypropyl)-3-(4-hydroxyphenyl)-2- azaspiro[3.4]octan-1-one were designed and synthesized. These analogs were found to lower total cholesterol (TC) and total glucose (TG) level in hamster serum via a high-cholesterol and high-fat feeding experiment. After four weeks of pre-feeding, total cholesterol (TC) lowering activity of spiro-β-lactam ezetimibe analogs were further improved, these analogs also will lower total cholesterol (TC) in the liver and total glucose (TG).The SAR studies suggest the advantage of N-phenyl onβ-lactam analogs, thus the existence of C3-phenyl is crucial for the activity of re-organized backbone analogs. Also the replacement of fluorophenyl substitutedβ-lactam by spiro-β-lactam have significant improvements in lowering the levels of TC and LDL-C in serum. And 2-(3-(4-fluorophenyl)-3-hydroxypropyl)-3-(4-hydroxyphenyl)-2-azaspiro[3.5]nonane-1-one is more active than 2-(3-(4-fluorophenyl)-3-hydroxypropyl)-3-(4-hydroxyphenyl)-2-azaspiro[3.4] octan-1-one. After further analysis of N1 SAR ofβ-lactam CAI, we speculate that the plane of a planar-structure substituent would form a certain conformation with theβ-lactam plane, and this conformation was beneficial for the inhibiting activity. To verify this assumption, we have designed and synthesizedβ-lactams with different C3 configurations to study SAR, and search for potent structure. With introduction of hydrogen bond and charge factors on theβ-lactams, novel azaspiro[3.5]nonane-1-one ezetimibe analogs were designed and synthesized for SAR study of cholesterol absorption inhibition. As the previous work suggests, the design of novel cholesterol absorption inhibitor will follow the methodology that the active functional side chains are rearranged on novel scaffold.In Chapter three, using the strategy as in chapter two, with retention of the important functional groups in ezetimibe, a series of non-β-lactam (imidazolidin-2-one and oxazolidinone) core ezetimibe analogs were designed and synthesized as cholesterol absorption inhibitors. Imidazolidin-2-one analogs were synthesized as follow: first the 1, 2-diamines were synthesized, followed by the transformation to imidazolidin-2-one core, alkylating the core with the alcohol fragment, and finally the deprotection of phenolic protecting group. Substituted oxazolidinones were synthesized through the reaction of benzyl and Boc-substituted aniline with benzaldehyde under n-butyl lithium, followed by alkylation with the alcohol fragment and deprotection of the phenolic protecting group. Imidazolidin-2-one analogs 1-(4-fluorophenyl)-3-(3-(4-fluorophenyl) -3-hydroxypropyl)-4-(4-hydroxyphenyl)imidazolidin-2-one and 3-(4-fluorophenyl)-1-(3- (4-fluorophenyl)-3-hydroxypropyl)-4-(4-hydroxyphenyl)imidazolidin-2-one showed significant effects in lowering the total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels in serum, as well as increasing high-density lipoprotein cholesterol (HDL-C) level. Also the imidazolidin-2-one core analogs were found to lower hamster liver total cholesterol (TC) and total glucose (TG).In chapter four, using the strategy as the second and third chapters, with retention of the important functional groups in ezetimibe, novel backbone ezetimebe analogs with potential inhibitory activity was designed. Unlike in previous chapters, in which the cores have been reported in other cholesterol absorption inhibitors, the core discussed in this chapter has been changed fromβ-lactam to isoindolinone. And 2-(3-(4-fluorophenyl)-3-hydroxypropyl)-3- (4-hydroxyphenyl)isoindolin-1-one was designed and synthesized. It was found that 2, 3-disubstituted isoindolinone will lower total cholesterol (TC) 31%, low-density lipoprotein cholesterol (LDL-C) 30% and total glucose (TG) 9% in hamster serum via a high-cholesterol and high-fat feeding experiment. The isoindolinone-ezetimibe mimic has considerable inhibitory activity. After four weeks of pre-feeding, the total cholesterol (TC) lowering activity of 2, 3-disubstituted isoindolinone was further improved, as well as total cholesterol in the liver (TC). Analogs with other heterocyclic cores were designed and synthesized.