Synthesis and Biological Evaluation of Novel 4′-Selenonucleosides

Abstract

A variety of modified nucleosides have been developed as biologically active compounds. Selenium, a bioisostere of oxygen and sulfur, is a crucial atom in human body. Modified nucleosides containing selenium have been studied from the past and various selenonucleosides have been synthesized as potent and bioactive compounds. This thesis describes the research on 4′-selenonucleosides, of which oxygen is replaced to selenium in the 4′-position of the sugar ring. First part of this thesis describes the synthesisof 4′-selenoadenosine and 4′-selenoguanosine. 4′-Se-purine nucleosides were synthesized under Vorbrüggen condition, whereas 4′-Se-pyrimidine nucleoside were synthesized using a Pummerer type condensation. 4-Selenosugar was not condensed with 6-Cl-purine under Pummerer type condensation condition, so 4-selenosugar was first acetylated. 4-Selenoacetate was used in the condensation reaction with TMSOTf as lewis acid. Both N7 and N9-conformers were formed in the condensation. I optimized to increase the ratio of N9 to N7 conformer, it was the best condition using toluene as solvent and heating at 100 oC. Also, the rearrangement of N7 to N9 conformer during condensation was proved by treating the separated N7 conformer with TMSOTf in toluene. Finally, I synthesized from 6-Cl-purine nucleoside to 4′-Se-adenosine and 4′-Se-inosine by using NH3/MeOH and 2-mercaptoethanol, respectively. 4′-Se-adenosine was confirmed by 1H NMR, 13C NMR and X-ray crystallography. 4′-Se-adenosine has northern and southern conformer in X-ray crystallography, it means the dynamic equilibrium of the conformers existing in solution state. In the second part, synthesis of a series of Se-IB-MECA, which is a bioisostere of IB-MECA and Thio-IB-MECA, is described. A series of N6-substituted-4′- selenoadenosine-5′-uronamides were synthesized starting from 4-selenosugar, and structure–activity relationships were studied at the human A3 and other subtypes of adenosine receptors (ARs). N6-iodobenzyl-4′-selenoadenosine-5′-uronamides (Se-IB-MECA, 4a) was a highly potent and selective agonist (Ki = 0.57 ± 0.100 nM ) at the human A3 AR, and most of synthesized compounds exhibited highly binding affinities at the human A3 AR. 5′-Methyluronamide derivatives were found to be full agonists in a cyclic AMP functional assay at the hA3 AR, while 5′-dimethyluronamide derivatives acted as antagonists in a functional assay. The last part of this thesis describes the synthesis of 2′-substituted-4′-selenopyrimidine nucleosides and its structure-activity relationships as anticancer agents. Based on the potent anticancer activity of araC with an arabino configuration at the 2′-position, novel 2′-substituted-4′-selenoarabinofuranosyl pyrimidines 3a-3u, with the fluoro and hydroxyl substitution were designed, synthesized, and evaluated for anticancer activity. The 2′-fluoro group was stereoselectively introduced through the double inversions of stereochemistry via the episelenium intermediate, which was formed by the participation of the selenium atom. Among the compounds tested, the 2′-fluoro derivative 3t was found to be the most potent anticancer agent and showed more potent anticancer activity than the control, araC. The anticancer activity of the 2′-arabino substitution is in the following order: 2′-F > 2′-OH.;변형핵산은 다양한 생리활성을 갖는 물질로서 여러 약물로 개발되고 있다. 셀레늄은 산소와 황과 주기율표상 같은 족에 속한 원소로, 생체내에서 필수적이다. 셀레늄을 포함한 변형 핵산은 과거부터 연구되어왔고, 다양한 생리활성을 가진 셀레늄 변형 핵산이 합성되었다. 이 학위 논문 에서는 셀레늄을 sugar 고리에서 4′번 위치의 산소와 치환한 물질에 대해 서술하였다. 첫번째로 4′-selenoadenosine과 4′-selenoguanosine의 개발에 대해 서술하였다. 4′-Se-pyrimidine nucleoside가 Pummerer 타입의 축합반응으로 합성되는 것과 달리, 4′-Se-purine nucleoside는 Vorbrüggen 조건 하에서 합성된다. 4-Selenosugars는 Pummerer 타입으로 6-chloropurine과 축합되지 않기 때문에 먼저 acetylation을 한 후 축합 반응을 진행하였다. 루이스 산으로 TMSOTf를 사용하여 축합 반응을 진행하면 N7-isomer와 N9-isomer가 동시에 얻어지는데, N7-isomer와 N9-isomer의 비율을 조절하기 위해 다양한 반응 조건으로 해보았다. 그 결과 toluene을 용매로 사용하고, 95 oC로 가열하였을 때 가장 높은 비율로 N9-isomer가 생성되었다. 또한 분리된 N7-isomer를 TMSOTf 존재 하에서 반응한 결과 N9-isomer로 모두 변화함을 관찰하였다. 이렇게 합성한 6-Cl-purine nucleoside에 NH3/MeOH과 2-mercaptoethanol를 처리하여 각각 4′-Se-adenosine과 4′-Se-guanosine을 얻었다. 분리 정제한 4′-Se-adenosine은 1H NMR, 13C NMR과 X-ray 결정 구조를 통해 분석하였는데 4′-Se-adenosine은 northern conformer와 southern conformer가 동적 평형을 이루며 존재한 다는 사실을 알아내었다. 두번째로 IB-MECA와 Thio-IB-MECA의 bioisostere인 Se-IB-MECA의 합성을 진행하였다. N6-substituted-4′-selenoadenosine-5′-uronamides는 4-selenosugar로부터 합성하였으며, 구조-활성 관계 연구를 수행하였다. N6-iodobenzyl-4′-selenoadenosine-5′-uronamides (Se-IB-MECA)가 사람 A3 아데노신 수용체에 가장 좋은 결합 친화력을 보여주었고, 대부분의 다른 유도체도 우수한 결합 친화력을 보였다. 5′-Methyluronamide는 cAMP functional assay를 통해 full agonist로 확인된 반면에, 5′-dimethyluronamide 유도체는 antagonist로 작용하였다. 마지막으로 2′-substituted-4′-selenopyrimidine nucleosides의 합성과 항암제로써 구조-활성 관계 연구를 수행하였다. arabino configuration를 가지는 araC가 항암 활성이 있음에 근거하여 2′ 위치에 플루오린과 hydroxyl를 도입시킨 새로운 2′-substituted-4′-selenoarabinofuranosyl pyrimidines 3a-3u를 설계하고 합성하였고, 그것의 항암 활성을 시험해보았다. 2′위치에 플루오린을 도입할 때 셀레늄 이온이 반응에 참여하여 episelenium 중간체를 거쳐 2′-fluoro-“up”물질이 합성된다. 항암 활성 테스트 결과 2′-fluoro 유도체인 3t가 가장 좋은 활성을 보였다. 2′- arabino 치환체의 항암활성 결과는 다음과 같은 순서를 따른다: 2′-F > 2′-OH.