Facile conversion of 23-hydroxyspirosolane into pregnane

Two novel reactions with regard to steroidal alkaloid sapogenols obtained from ripe tomato have been found. These reactions have been attained by simple facile method in only refluxing with pyridine and water. One is isomerization of a spirosolane derivative, isoesculeogenin A (2), into a rare solanocapsine derivative, esculeogenin B (3), disclosing a chemical correlation between isoesculeogenin A and esculeogenin B. Another is conversion of a 23-hydroxyspirosolane derivative, esculeogenin A (1), into a pregnane derivative (4), presenting an epoch-making method for derivation of steroidal hormone material.     

利用薯蓣皂甙元完整骨架形式合成1α,25-二羟基维生素D3

首次利用薯蓣皂甙元的完整骨架经16步反应以7.6%的总收率合成了骨化三醇(1α,25-二羟基维生素D₃)的光化反应前体. 3-苄基保护的薯蓣皂甙元经还原开E/F环产生3,16,26-胆甾三醇-3-苄醚(5). 除去化合物5 C-16羟基后, 其C-26羟基经消除和羟基化反应转移到C-25位. 目标分子A/B环结构单元通过薯蓣皂甙元A/B环的官能团转化被构筑. 按照已知的光化反应, (1S,3R)-胆甾-5,7-二烯-1,3,25-三醇能被转化成为1α,25-二羟基维生素D₃.     

Synthesis of new di- and triamine diosgenin dimers

In this study, a high yield synthesis of symmetrical steroidal polyamine dimers was achieved by the dimerization of (25R)-3β-acetoxyfurost-5-en-26-al via several di- and triamine linkers under mild conditions. To ensure the dimerization via E-E ring, the hydroxyl group in diosgenin was protected by an acetyl group. The important step is opening the spiroketal moiety using NaCNBH₃/AcOH to furnish the primary alcohol at C-26, followed by oxidation using PCC/CH₂Cl₂ to synthesize the desired aldehyde. Finally, reductive amination with diaminopropane, diaminobutane, diaminohexane, and spermidine using Na(OAc)₃BH as reducing agent, afforded the required four dimers.     

Efficient, one-pot transformation of indoles into functionalized oxindole and spirooxindole systems under Swern conditions

The reaction of indole derivatives bearing a 3- or 4-hydroxyalkyl chain with dimethylsulfoxide and oxalyl chloride under Swern conditions led to a one-pot, three-component process involving three different synthetic transformations, namely oxidation of indole to oxindole, introduction of a chlorine substituent at the oxindole C-3 position and substitution of the hydroxyl group in the side chain by chlorine, in good to excellent overall yields. The same conditions, applied to a 2-methylindole, afforded a 2-formylindole derivative oxidized at its side chain. The reaction starting from one indole with a 2-hydroxyalkyl chain furnished 3-(2-hydroxyalkyl)oxindoles. Finally, application of the Swern conditions to derivatives of indole-3-propionic or -butyric acid afforded 3-spirooxindole lactones.     

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.     

Conversion of Some 2(3H)‐Furanones into Pyrrolinotriazine and Oxazolopyrimidine Derivatives

2(3H)‐Furanones 1 were utilized for the construction of pyrrolinotriazine and oxazolopyrimidine derivatives 4 and 9 . Thus, 1 reacted with glycine in ethanol at 70°C to give the acids 2 , which were cyclized into the pyrrolin‐5‐one derivatives 3 by the action of HCl/AcOH. The later compounds 3 were also obtained by refluxing the furanones 1 with glycine in glacial AcOH for 10 h. The carboxy functionality in 3 was used for the construction of a triazinone ring by treatment with thionyl chloride followed by refluxing the acid chloride with hydrazine in ethanol. The conversion of the furanones 1 into the oxazolopyrimidine derivatives 9 involved the following steps: (i) ring opening of the lactone ring with hydrazine hydrate to give the acid hydrazides 5 , (ii) conversion of the hydrazides 5 into the corresponding acyl azides 6 by action of NaNO2/AcOH, (iv) base‐catalyzed decomposition of the azides in the presence of glycine, (v) ring closure of the urea derivatives 7 into the pyrimidine derivatives 8 , and finally (vi) condensing 8 with benzaldehyde in the presence of NaOAc/AcOH mixture.     

Alpha-hydroxylation at C-15 and C-16 in cholesterol: synthesis of (25R)-5alpha-cholesta-3beta,15alpha,26-triol and (25R)-5alpha-cholesta-3beta,16alpha,26-triol from diosgenin

[reaction: see text] (25R)-5alpha-cholesta-3beta,16alpha,26-triol 7b and (25R)-5alpha-cholesta-3beta,15alpha,26-triol 10b were synthesized, via (25R)-5alpha-cholesta-3beta,16beta,26-triol 5a, from diosgenin 3 in 52% yield over six steps and 47% yield over eight steps, respectively. An efficient method for inversion of a C-16beta hydroxyl to the C-16alpha position and a short method for transposition of a C-16beta hydroxyl to the C-15alpha position via the unexpected beta-reduction of a C-15 ketone in a steroid are reported.     

Synthesis and Kinetic Evaluation of Inhibitors of the Phosphatidylinositol-Specific Phospholipase C from Bacillus cereus

Substrate analogues of phosphatidylinositol (1) were synthesized and evaluated as potential inhibitors of the bacterial phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus cereus. The chiral analogues of the water-soluble phospholipid substrate 5 were designed to probe the effects of varying the inositol C-2 hydroxyl group, which is generally believed to serve as the nucleophile in the first step of the hydrolysis of phosphatidylinositols by PI-PLC. In the analogues 6-9, the C-2 hydroxyl group on the inositol ring of the phosphatidylinositol derivatives was rationally altered in several ways. Inversion of the stereochemistry at C-2 of the inositol ring led to the scyllo derivative 6. The inositol C-2 hydroxy group was replaced with inversion by a fluorine to produce the scyllo-fluoro inositol 7 and with a hydrogen atom to furnish the 2-deoxy compound 8. The C-2 hydroxyl group was O-methylated to prepare the methoxy derivative 9. The natural inositol configuration at C-2 was retained in the nonhydrolyzable phosphorodithioate analogue 10. The inhibition of PI-PLC by each of these analogues was then analyzed in a continuous assay using D-myo-inositol 1-(4-nitrophenyl phosphate) (25) as a chromogenic substrate. The kinetic parameters for each of these phosphatidylinositol derivatives were determined, and each was found to be a competitive inhibitor with K(i)'s as follows: 6, 0.2 mM; 10, 0.6 mM; 8, 2.6 mM; 9, 6.6 mM; and 7, 8.8 mM. This study further establishes that the hydrolysis of phosphatidylinositol analogues by bacterial PI-PLC requires not only the presence of a C-2 hydroxyl group on the inositol ring, but the stereochemistry at this position must also correspond to the natural myo-configuration. For future inhibitor design, it is perhaps noteworthy that the best inhibitors 6 and 10 each possess a hydroxyl group at the C-2 position. Several of the inhibitors identified in this study are now being used to obtain crystallographic information for an enzyme-inhibitor complex to gain further insights regarding the mechanism of hydrolysis of phosphatidylinositides by this PI-PLC.     

C-lactam derivatives of oleanolic acid. The synthesis of C-lactam by Beckmann rearrangement of C-oxime

Oleanolic acid, one of the most known triterpenes, was subjected to different chemical transformations within C-3 beta-hydroxyl group, a double bond between C-12 and C-13, and a carboxyl function at C-17 in order to obtain new derivatives. The key compound consists of four six-membered rings (A, B, D, E) and one enlarged ring (C ring) containing a nitrogen atom and a carbonyl function - lactam. This type of derivative can be obtained by Beckmann rearrangement of the appropriate oxime. The lactam can be transformed into thiolactam with the use of Lavesson's reagent. The method is also presented for new derivatives synthesis, as well as their structure elucidation by spectroscopic means.     

Facile construction of 1,2-cis glucosidic linkage using sequential oxidation-reduction route for synthesis of an ER processing α-glucosidase I substrate

The fluorescence-labeled hexasaccharide (Glcα1-2Glcα1-3Glcα1-3Manα1-2Manα1-2Manα) was synthesized as a substrate for the processing enzyme α-glucosidase I. To construct the 1,2-cis glucosidic linkages, we employed an α stereoselective coupling using the mannosyl donor by assisted neighboring-group participation, followed by conversion of the stereochemistry of the C-2 hydroxyl group in the mannose residue using sequential oxidation of C-2 hydroxyl group to a 2-keto group and stereoselective reduction of the hydroxyl group to the gluco-configuration to provide the corresponding α-glucoside derivative. Using this strategy, the three consecutive α-glucosidic linkages were easily obtained in a stereoselective manner. Finally, the Dansyl labeled hexasaccharide derivative was used to measure the activity of processing α-glucosidase I.     

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.     

The assignment of IR absorption bands due to free hydroxyl groups in cellulose

Interpretation of the IR hydroxyl absorption bands in cellulose has been limited to the inter- and intramolecularly hydrogen-bonded hydroxyl groups in the crystalline form. This paper attempts to assign IR frequencies due to ‘free‘ or non-hydrogen bonded hydroxyl groups by using a curve fitting method. The almost completely methylated cellulose derivatives of tritylcellulose (previously used in related studies) exhibited small IR bands due to hydroxyl groups. The IR bands were assumed to appear under stereohindered conditions and thus resulted in a mixture of bands which included the contribution of free hydroxyl groups. The curve fitting method deconvoluted the IR bands into three bands in the OH stretching region: they were interpreted in terms of free or hydrogen bonded hydroxyl groups. The assignments were confirmed by comparison of an almost completely methylated derivative with partially methylated derivatives having different degrees of substitution. In addition, intramolecular hydrogen bonds involving OH at the C-3, C-2 and C-6 positions were shown to be easily formed, even between extremely small numbers of unsubstituted hydroxyl groups present, and thus cause perturbation of the specific deconvoluted band. This revised version was published online in August 2006 with corrections to the Cover Date.     

利用脱镁叶绿酸甲酯的化学修饰合成红紫素酰亚胺衍生物

A series of novel purpurin-18 imide derivatives exhibiting long wavelength absorption and amphiphilicity wereobtained from methyl pheophorbide-a(MPa)by modification of the peripheral functional groups.The vinyl groupat 3-position was oxidized with OsO_4 and NaIO_4 to form the formyl group and the Grignard reaction of this alde-hyde with the alkyl magnesium bromide was carried out to give the corresponding 3-(1-hydroxylalkyl)pheophor-bide-a.The E-ring of these chlorines was converted into anhydride ring to give purpurin derivatives by air oxidation.The trans-3~2-alkyl purpurin derivatives were obtained by dehydration of hydroxyl group at 3~1-position.TheN-hydroxyl purpurin imide was generated by treatment of the anhydride ring with bydroxylamine hydrochloride.The 3~1-alkylacyl-N-hydroxyl purpurin imides were obtained by oxidation of hydroxyl group at 3~1-position.Theacylation of N-hydroxyl group was completed to afford N-acyloxy purpurin imides.The photocytoxicity of severalcompounds in vitro were tested.     

A facile and efficient method for the synthesis of solasodine from diosgenin

A facile and high-yielding route for the synthesis of solasodine from diosgenin is devised. Ring opening of steroidal spiroketal under mild conditions with trifluoroacetyl trifluoromethanesulfonate (TFAT) provides an applicable protocol to prepare key intermediates 4 or 3-Ac-solasodine, which can potentially serve as a platform for the selective functionalization of C(3)-OH and N-H of solasodine. The simple operations without purification by column chromatography make this method suitable to scale up.     

Straightforward synthesis of thiodisaccharides by ring-opening of sugar epoxides

3,4-Anhydro hexopyranosides have been prepared by diastereoselective epoxidation of derivatives of 2-propyl 3,4-dideoxy-alpha-D-erythro-hex-3-enopyranoside (5), selectively protected at HO-2 and HO-6. The allylic group at C-2, in 5 and derivatives, plays a critical role in the facial selectivity of the epoxidation reaction. Thus, the free HO-2 in 3 (the 6-O-acetyl derivative of 5) directs the attack of m-chloroperbenzoic acid from the more hindered alpha face of the molecule to give 2-propyl 6-O-acetyl-3,4-anhydro-alpha-D-allopyranoside (7) accompanied by the beta epoxide 6 as a very minor product. Reverse diastereoselectivity has been obtained when the HO-2 in 3 was substituted by a bulky tert-butyldimethylsilyl (TBS) group. In this case, the major isomer was the 2-O-TBS derivative of 6 (alpha-D-galacto configuration). The ring-opening of sugar epoxides by nucleophilic per-O-acetyl-1-thio-beta-D-glucopyranose (11) was employed as a convenient approach to the synthesis of (1-->3)- and (1-->4)-thiodisaccharides. For example, ring-opening of the oxirane 7 by 11 led to the expected regioisomeric per-O-acetyl thiodisaccharides beta-D-Glc-S-(1-->3)-4-thio-alpha-D-Glc-O-iPr (12) and beta-D-Glc-S-(1-->4)-4-thio-alpha-D-Gul-O-iPr (13). Regioselectivity in the construction of the (1-->4)-thioglycosidic linkage could be achieved by hindering C-3 of the 3,4-anhydro sugar with a bulky silyloxy group at the vicinal C-2. For instance, coupling of the 2-O-TBS derivative of 7 with 11 led regioselectively to the protected thiodisaccharide beta-D-Glc-S-(1-->4)-4-thio-alpha-D-Glc-O-iPr (27). The utility of the approach was demonstrated through the synthesis of sulfur-linked analogues of naturally occurring (laminarabiose and cellobiose) and non-natural disaccharides (i.e., beta-D-Glc-(1-->4)-alpha-D-Gul).     

Solution- and solid-phase, modular approaches for obtaining different natural product-like polycyclic architectures from an aminoindoline scaffold for combinatorial chemistry

With the goal of developing a modular approach leading to different indoline alkaloid natural-product-like tricyclic derivatives having an unsaturated lactam (see compounds 13, 14, and 16), an aminoindoline-based bicyclic scaffold 10 was obtained from 9. The selective deprotection of the indoline NTeoc or benzylic NHAlloc in compound 10, followed by N-acryloylation and then subjection to a ring-closing metathesis reaction, successfully led to obtaining two different architectures (13/14 and 16) having an unsaturated lactam functionality. This modular solution-phase methodology was then developed on solid phase. To achieve this objective, the aminoindoline bicyclic scaffold having an additional hydroxyl group could be immobilized onto the solid support using alkylsilyl linker-based polystyrene macrobeads, giving 18. By applying a ring-closing metathesis approach, 20 (tricyclic derivative with seven-membered-ring unsaturated lactam) and 23 (tricyclic derivative with eight-membered-ring unsaturated lactam) were then obtained from 18 in a number of steps.     

A short and economical synthesis of orthogonally protected C-linked 2-deoxy-2-acetamido-alpha-D-galactopyranose derivatives

A short and high-yielding synthesis has been devised to prepare C-linked 2-deoxy-2-acetamido-alpha-D-galactopyranose derivative 3. One of the main advantages of this approach is that it employs commercially available and inexpensive d-glucosamine as the starting material. The key steps include a highly stereoselective C-allylation followed by epimerization of the C-4 hydroxyl group. Building block 3 and orthogonally protected C-linked 2-deoxy-2-acetamido-alpha-D-galactopyranose derivative 2 were obtained in 44% overall yield (six steps) and 29% overall yield (eight steps), respectively. This represents a significant improvement over previously reported syntheses.     

Nickel-catalyzed coupling producing (2Z)-2,4-alkadien-1-ols, conversion to (E)-3-alkene-1,2,5-triol derivatives, and synthesis of decarestrictine D

The 3-alkene-1,2,5-triol structure is not only a major framework of biologically important molecules but also a new functional-group-rich unit for synthesis of polyols and sugars. A method furnishing such triol derivatives 8 was developed and successfully applied to synthesis of decarestrictine D (18). First, coupling reaction of the unprotected alcohols 2 with borates 4 was investigated to produce the dienyl alcohols 6 with NiCl2(dppf) in Et2O/THF (5:1) at room temperature. The hydroxyl-group-directed epoxidation of 6 followed by palladium-catalyzed reaction with AcOH (Scheme 1) furnished 3-alkene-1,2,5-triol derivatives 8. Since each step proceeded with high stereo- and regioselectivities, the stereochemistry of 8 has been correlated with the olefin geometry of 6. With the above transformation in mind, synthesis of the full carbon skeleton of decarestrictine D (18) could be designed easily and was completed successfully. Furthermore, a new seco acid 19b with the MOM protective group for the three hydroxyl groups was found to afford macrolide 48 in a yield higher than those reported previously.     

Synthesis and antioxidant capacity of 5-selenopyranose derivatives

Described is a convenient method for the syntheses of sulfur and selenium containing carbohydrate derivatives of L-gulodeoxynojirimycin and the corresponding C-5 epimer D-mannodeoxynojirimycin. The key step in the synthesis of the latter involves epimerisation of the C-5 hydroxyl group by an oxidation followed by stereo-selective reduction to obtain the desired D-sugar derivative. Both derivatives displayed a dose-dependent prevention of the oxidation of methionine residues on human plasma proteins induced by the inflammatory oxidant hypochlorous acid. The seleno-analogues were considerably more active than their thio-equivalents.     

Synthesis of 5-acetyloxazoles and 1,2-diketones from β-alkoxy-β-ketoenamides and their subsequent transformations

Lithiated alkoxyallenes, nitriles, and carboxylic acids have been employed as precursors in a three-component reaction leading to highly substituted β-alkoxy-β-ketoenamides. Upon treatment with trifluoroacetic acid, these enamides could be easily cyclized to 5-acetyloxazole derivatives. The synthesis is very flexible with respect to the substitution pattern at C-2 and C-4 of the oxazole core. A mechanistic suggestion for the oxazole formation is presented on the basis of (18)O-labeled compounds and their mass spectrometric analysis. In several cases, 1,2-diketones are formed as side products or even as major components. The acetyl moiety at C-5 of the oxazole derivatives can efficiently be converted into alkenyl or alkynyl moieties, which allows a multitude of subsequent reactions. Condensation reactions of the acetyl group provided the expected oxime or hydrazone. By applying a Fischer reaction, the phenylhydrazone could be transferred into an indole, which emphasizes the potential of 5-acetyloxazoles for the preparation of highly substituted (poly)heterocyclic systems. The alkynyl group at C-2 is prone to addition reactions, providing an enamine with interesting photophysical properties. Sonogashira couplings were performed with 5-alkynyl-substituted oxazoles, furnishing the expected aryl-substituted products. This alkynyl unit was employed for the preparation of a new, star-shaped trisoxazole derivative. The ability of this multivalent compound to form self-assembled monolayers between the basal plane of highly oriented pyrolytic graphite and 1-phenyloctane was demonstrated by scanning tunneling microscopy (STM). The star-shaped compound seems to prefer the C(3)-symmetric arrangement in this two-dimensional crystal. Two 1,2-diketones were smoothly converted into functionalized quinoxaline derivatives.