Synthesis of 8-(omega-Hydroxyalkyl)-, 8-(omega-hydroxyalk-1-enyl)-, and 8-(omega-hydroxyalk-1-ynyl)adenines using the tert-butyldimethylsilyloxymethyl group, a new and versatile protecting group of adenine

The synthesis of 12 analogues of adenine substituted at C-8 by an omega-hydroxyalkyl, omega-hydroxyalk-1-enyl, or omega-hydroxyalk-1-ynyl chain of various length has been carried out in five or six steps starting from adenine. The analogues were obtained using a new protecting group of adenine, the tert-butyldimethylsilyloxymethyl group. 9-tert-Butyldimethylsilyloxymethyl-adenine is more soluble than adenine in organic solvents. It was prepared regiospecificaly in two steps from adenine and was amenable to C-8 iodination under basic conditions and to subsequent introduction of the various carbon chains at C-8 by palladium-catalyzed cross-coupling reactions (Stille or Sonogashira). The protecting group was removed under acidic conditions, thus demonstrating its versatility.     

Total synthesis of Bengamide E and analogues by modification at C-2 and at terminal olefinic positions

[Reaction: see text]. The total synthesis of the natural product Bengamide E, one of the members of a new class of antitumor natural products of marine origin, is reported based on a convergent and flexible synthetic route featuring an oxirane ring-opening reaction and an olefin cross metathesis. In a similar way, analogues structurally modified at C-2 and at the terminal vinyl positions were prepared by introduction of various nucleophiles and alkyl substituents during the epoxide opening and the olefin cross metathesis steps, respectively. These studies demonstrate the validity of our synthetic strategy, although they reveal some problems associated with the olefin cross metathesis, whose efficiency depends on the substituent at the C-2 position as well as the steric environment of the alkene.     

Utility of the ammonia-free Birch reduction of electron-deficient pyrroles: total synthesis of the 20s proteasome inhibitor, clasto-lactacystin beta-lactone

A new synthesis of the 20S proteasome inhibitor clasto-lactacystin beta-lactone is described. Our route to this important natural product involves the partial reduction of an electron deficient pyrrole as a key step. By judicious choice of enolate counterion, we were able to exert complete control over the stereoselectivity of the reduction/aldol reaction. Early attempts to complete the synthesis by using a C-4 methyl substituted pyrrole are described in full, together with our attempts to promote regioselective elimination of a tertiary alcohol. The lessons learnt from this first approach led us to develop another, and ultimately successful, route that introduced the C-4 methyl group at a late stage in the synthesis. Our successful route is then described and this contains several highly stereoselective steps including a cis-dihydroxylation and an enolate methylation. The final synthesis proceeds in just 13 steps and in 15 % overall yield making it an extremely efficient route to this valuable compound.     

Asymmetric total syntheses of (-)-jorumycin, (-)-renieramycin G, 3-epi-jorumycin, and 3-epi-renieramycin G

The total synthesis of (-)-jorumycin (1) and (-)-renieramycin G (2) has been accomplished in 25 and 23 steps, respectively, from 5-benzyloxy-2,4-dimethoxy-3-methyl-benzyl alcohol. The synthesis features a substrate-tunable stereoselective intramolecular Pictet-Spengler-type reaction for the construction of the key pentacyclic core of both targets, bearing either the natural configuration or the epimeric configuration at C-3. With access to a C-3 epi-pentacyclic framework, 3-epi-jorumycin (32) and 3-epi-renieramycin G (34) were also successfully synthesized. Furthermore, preliminary biological evaluation of 3-epi-jorumycin (32), in addition to relevant synthetic intermediates, revealed that significant cytotoxicity had been retained in these compounds. Therefore, these early studies constitute the basis for a new structure activity relationship (SAR) investigation for this class of antitumor antibiotics.     

左氧氟沙星的噻唑并均三唑衍生物的合成及抗肿瘤活性

为进一步发展抗菌药氟喹诺酮向抗肿瘤活性转化的有效结构修饰策略,基于药效团骨架的迁越药物设计原理,用噻唑并均三唑稠环取代左氧氟沙星(1)C-3羧基的等排体,α,β-不饱和酮为其修饰基,设计合成了C-3噻唑并均三唑稠杂环目标化合物(6a-6l)。 体外抗肿瘤活性结构表明,所合成的12个化合物的活性均强于母体左氧氟沙星,化合物6e、6i、6j的活性与对照抗肿瘤药阿霉素相当。 因此,α,β-不饱和酮修饰的均三唑骨架替代C-3羧基有利于提高氟喹诺酮的抗肿瘤活性。     

Establishing the absolute configuration of the asbestinins: enantioselective total synthesis of 11-acetoxy-4-deoxyasbestinin D

A highly stereoselective synthesis of 11-acetoxy-4-deoxyasbestinin D (1) has been completed in 26 linear steps. The synthesis hinges on a selective glycolate aldol addition to establish the C-2 stereocenter, a ring-closing metathesis reaction to complete the oxonene, and an intramolecular Diels-Alder cycloaddition to establish the relative configuration at C-1, C-10, and C-14. This initial total synthesis of an asbestinin also serves to confirm the absolute configuration of this subclass of the C-2-C-11-cyclized cembranoid natural products.     

Diastereoselective reactions at enantiomerically pure, sterically congested cyclohexanes as an entry to wailupemycins A and B: total synthesis of (+)-wailupemycin B

Wailupemycin A (1) and B (2) are polyketide natural products with a highly substituted cyclohexanone core. Three different routes for the syntheses of these compounds were pursued, which commenced from either (R)-(-)-carvone (ent-5) or (S)-(+)-carvone (5). In the first approach it was attempted to construct the skeleton of wailupemycin A from triol 19 (nine steps from ent-5; 19 % yield) by a sequence of diastereoselective epoxidation, nucleophilic ring opening at C-13 and carbonyl addition at C-5. The synthetic plan failed at the stage of the carbonyl addition to aldehyde 27, which had been obtained in seven steps (18 % yield) from triol 19. The second route included an epoxide ring opening at C-13 and a carbonyl addition at C-7 as key steps. It could have led to either wailupemycin A or B depending on the diastereoselectivity of the addition step. Starting from allylic alcohol 30 (six steps from ent-5; 59 % yield) the cyclohexanone 28 was obtained in five steps (54 % yield). Unfortunately, the carbonyl addition failed also in this instance. In the eventually successful third attempt the skeleton of wailupemycin B was built from cyclohexanone 43 (eight steps from 5; 53 % yield) by highly diastereoselective carbonyl addition reactions at C-7 and C-12. The phenyl group at C-14 was introduced at a late stage of the synthetic sequence. Careful protecting group manipulation finally allowed for the total synthesis of (+)-wailupemycin B. The absolute and relative configuration of the natural product was unambiguously confirmed. The total yield of wailupemycin B amounted to 6 % over 23 steps starting from (S)-(+)-carvone (5).     

The First Efficient Approach from α-(-)-Santonin to Dihydroagarofuran Sesquiterpene

The naturally occurring dihydroagarofuran compounds have been demonstrated to show some important bioactive activities, such as insect antifeedant, antitumor activities.¹ Synthetic research of this kind of compounds have been attracting the increasing interest of organic chemists. Because a total synthesis of polyol skeleton involved too many steps,² our synthetic efforts are focusing on search for a short and efficient approach and thus, we begin with readily available α-(-)-santonin(1). The creative key steps include generation of C₅-OH, the stereochemical reversion at C-7 and the cyclization of tetrahydrofuran. A successful approach is shown in the following scheme.     

Synthesis of the shark repellent pavoninin-4

[reaction: see text] The first synthesis of the shark repellent pavoninin-4, 3, was achieved in 12 steps with 21% overall yield from diosgenin, 8. Key reactions involve an efficient synthesis of the C-15alpha hydroxyl steroid from a C-16beta hydroxyl steroid by an unexpected 1,2-transposition strategy, a stereospecific glycosylation of a hindered C-15alpha alcohol using glycosyl fluoride as a glycosyl donor and a highly chemoselective acetylation of the C-26 primary alcohol by catalytic transesterification.     

Synthesis of lanosterol derivatives with a functional group at C-32, including an antineoplastic sterol, 3 beta-hydroxylanost-7-en-32-oic acid

Lanosterol derivatives with a functional group at C-32 have been synthesized from 3 beta-acetoxylanostan-7 alpha-ol. The key reaction of the synthesis is the hypoiodite reaction of 3 beta-acetoxylanostan-7 alpha-ol. In vitro antitumor activity testing of the lanosterol derivatives revealed that 3 beta-hydroxylanost-7-en-32-oic acid has antineoplastic activity.     

First total synthesis of JS isoprostane

A stereoselective Julia-Lythgoe olefination followed by an efficient 1,3-allylic transposition of the C-9 hydroxyl group of compound 13 has allowed the first total synthesis of J(2) isoprostane (1), a recently discovered member of the growing isoprostane family. This elusive compound opens up numerous new avenues for the molecular biology of cyclopentenone prostaglandins which are endowed of intriguing biological effects such as antitumor, antiinflammatory, and antiviral activities. In principle, our approach is flexible enough to allow an easy synthesis of other isoprostanes of the J family following the same methodology.     

N-(5-芳苄叉基饶丹宁)左氧氟沙星酰胺的合成及抗肿瘤活性

为进一步发现氟喹诺酮药物向抗肿瘤活性转化的结构修饰新策略,用酰氨基为左氧氟沙星(1)C-3羧基的电子等排体,5-芳苄叉基饶丹宁为其功能修饰基,设计合成了N-(5-芳苄叉基饶丹宁)左氧氟沙星酰胺类目标化合物(6a-6n)。 体外抗肿瘤活性结果表明,所合成的14个化合物的活性均强于母体左氧氟沙星,且对正常细胞表现出较低的细胞毒性作用。 构效关系表明,增大芳基取代基的体积或供电性均导致抗肿瘤活性的明显降低,反之,吸电子取代苯基或芳香杂环类目标化合物的抗肿瘤活性强于其他取代基类。 其中,硝基化合物6l、呋喃6m和吡啶6n对人胰腺癌细胞株(Capan-1)的半数抑制浓度(IC₅₀) 与对照抗肿瘤药阿霉素(1.6 μmol/L)相当,分别为1.8、0.8和1.3 μmol/L。 因此,芳苄叉基饶丹宁修饰的酰氨基替代C-3羧基有利于提高氟喹诺酮的抗肿瘤活性。     

Regioselectivity of Pictet-Spengler cyclization reactions to construct the pentacyclic frameworks of the ecteinascidin-saframycin class of tetrahydroisoquinoline antitumor antibiotics

The regiochemical outcome of Pictet-Spengler cyclization reactions directed toward the preparation of the pentacyclic core of the ecteinascidin class of antitumor antibiotics has been investigated on two different phenolic substrates. In one substrate, the assistance of an incipient benzylamine group at C-4 is postulated to direct the cyclization in favor of the pentacyclic framework of ET-743, which bears a hydroxyl group at C-18. Conversely, cyclization of an alternative substrate lacking a heteroatom at C-4 favors the opposite regiochemical outcome, primarily affording an unnatural pentacyclic core bearing a hydroxyl group at C-16.     

An isofagomine analogue with an amidine at the pseudoanomeric position

(3R,4R,5R)-2-Imino-3,4-dihydroxy-5-hydroxymethylpiperidine hydrocloride or isofagomidine was synthesized from D-arabinose in 12 steps and an overall yield of 9.9%. The synthesis proceeded by introduction of an aminomethyl group in the 4-position of D-arabinose and conversion of C-1 into a nitrile. The key step in the synthesis was a copper-catalyzed cyclization of aminonitrile to amidine. Isofagomidine was a potent α-mannosidase inhibitor (K(i) = 0.75 μM).     

Asymmetric synthesis of (2S,3R)-(−)-epi-CP-99,994 using sulfinimine-derived anti-2,3-diamino esters

A differentially protected C-3 N-sulfinyl, C-2 N,N-(diphenylmethylene) 2,3-diamino ester was employed in the synthesis of the amino piperidine (2S,3R)-(−)-epi-CP-99,994. Key steps in the synthesis included the chemoselective hydrolysis of the C-2 N,N-(diphenylmethylene) group and its reprotection as a dibenzylamino group.     

抗革兰氏阴性菌耐格霉素的形式合成

耐格霉素是具有抗革兰氏阴性菌活性的天然产物.以廉价易得的3-羰基-4-氯丁酸乙酯为原料,以八步29%的总收率实现了耐格霉素的形式合成.该工作改进了文献的合成路线,利用生物催化不对称还原高立体选择性引入C-5位的手性羟基,并将危险的叠氮引入反应放在合成后期,降低合成路线的操作风险.分子中C-3位的仲碳胺基手性中心通过Ellamn试剂介导的不对称Mannich反应构建.该路线易于放大,有望为构建耐格霉素类似物分子库以及高通量药物筛选奠定基础.     

饶丹宁甲叉基取代左氧氟沙星衍生物的合成与抗肿瘤活性

为寻找提高氟喹诺酮肿瘤活的有效结构修饰策略,左氧氟沙星(3)的衍生物(S)-(-)-9-氟-2,3-二氢-3-甲基-10-(4-甲基-1-哌嗪基)-[1,4]噁嗪并[2,3,4-ij]-喹啉-7(4H)-酮-6-甲醛(5)与饶丹宁类(2a-2l)通过Claisen-Schmid缩合反应构建了饶丹宁甲叉基取代左氧氟沙星衍...     

Total synthesis of (+)-tedanolide

A convergent, stereocontrolled total synthesis of (+)-tedanolide (1), an architecturally complex marine antitumor macrolide, has been achieved in 31 steps (longest linear sequence). Highlights of the synthesis comprise a highly efficient dithiane union, followed by an Evans-Tishchenko "oxidation" to enable formation of the seco-ester in the presence of an oxidatively labile dithiane, a highly refined protecting group strategy, and a chemo- and stereoselective epoxidation at C(18,19).     

Total synthesis of epothilone A

[reaction: see text]Epothilones A (1) and B (2) are potent antitumor natural products with a Taxol-like mechanism of action. A total synthesis of epothilone A (1) is reported, which utilized chiral silane-based bond construction methodology to introduce the key C-6 and C-7 stereocenters of fragment 4. The C-15 stereocenter of fragment 5 was established by a lipase-mediated kinetic resolution. The fragments were assembled with a Suzuki coupling reaction and an aldol condensation and cyclized with a Yamaguchi-type macrolactonization reaction.     

Synthesis of castanospermine

The diastereoselective synthesis of castanospermine is described in 11 synthetic steps from l-xylose. The borono-Mannich reaction between l-xylose, allylamine, and (E)-styrene boronic acid gives a tetrahydroxy amine with the desired configurations for C-6, C-7, C-8, and C-8a in the target molecule. A novel pyrrolo[1,2-c]oxazol-3-one precursor was employed to allow for the control of π-facial diastereoselectivity in an osmium(VIII)-catalyzed syn-dihydroxylation (DH) reaction. A regioselective ring-opening of the cyclic sulfate derivative of the resulting diol then secured the C-1 hydroxyl group of castanospermine with the correct configuration. A Mitsunobu cyclization then provided di-O-benzyl castanospermine and ultimately the final target alkaloid.