石杉碱甲结构改造的研究进展

石杉碱甲是高效、高选择性的可逆性乙酰胆碱酯酶抑制剂,是治疗早老性痴呆症的一个有前景的药物.本文概述了石杉碱甲的性质、结构和构效关系,从结构简化、C10、吡啶酮环、脂桥环、环外双键和桥头氨基等方面综述了石杉碱甲结构改造的研究进展,并描述了所得的新型石杉碱甲类似物的抗乙酰胆碱酯酶的生物活性.在已合成的大量的石杉碱甲类似物中,部分类似物的活性优于天然石杉碱甲,石杉碱甲结构改造的研究取得了可喜的进展.     

Synthesis, receptor binding affinities and conformational properties of cyclic methylenedithioether analogues of angiotensin II

Cyclic 12-, 13- and 14-membered ring angiotensin II analogues related to disulfides but encompassing methylene-dithioether bridges have been prepared. The affinity data from these derivatives were compared to those from the disulfides. The methylenedithioether analogues displayed good binding affinities to rat liver AT1 receptors although in most cases somewhat lower than their disulfide counterparts. One of the methylenedithioethers with a 13-membered ring system demonstrated the highest binding affinity among the thioethers. Theoretical conformational analysis of model compounds of the two series were performed suggesting a similarity between the disulfide and the corresponding methylenedithioether analogues and also between the ring size homologues. This analysis also suggested that some of the model compounds were prone to adopt inverse gamma-turn conformations, which was further supported by use of NMR spectroscopy of the 12-membered ring analogue in the series. The easily executed methylenedithioether cyclization should constitute a valuable complement to the common disulfide methodology for fine-tuning and for probing the bioactive conformation of peptides.     

Structural and stereospecific requirements for the nucleoside-triggered germination of Bacillus cereus spores

A selection of adenosine analogues was tested for their ability to trigger germination of Bacillus cereus NCIB 8122 spores. The germination-inducing activity was governed by the structural properties of the sugar rather than the base moieties of the nucleosides. Among the sugar-modified analogues, only those containing a 2'-deoxy-D-ribose moiety promoted spore germination. Requirements for a specific molecular structure of the base were not clearly identified, although the highest activity was observed when substituents were inserted at position 6 of the purine ring. All the base-modified analogues, even those such as coformycin and 2'-deoxycoformycin with an expanded base ring, retained the germination-inducing activity of adenosine. However, of the two 2'-deoxycoformycin diastereoisomers characterized by an asymmetric carbon atom at position 8 of the homopurine ring, only the 8S-isomer induced germination, thus indicating that stereospecific configuration of the inducer, at least in the case of 2'-deoxycoformycin, appears to be essential for the initiation of spore germination. The differences in the germination-inducing activity of the various analogues tested were not affected significantly by spore activation at different temperatures, although the higher the activation temperature, the lower was the concentration of each analogue required for maximum germination.     

RCAI-8, 9, 18, 19, and 49-52, conformationally restricted analogues of KRN7000 with an azetidine or a pyrrolidine ring: Their synthesis and bioactivity for mouse natural killer T cells to produce cytokines

Conformationally restricted analogues of KRN7000, an alpha-d-galactosyl ceramide, were synthesized to examine their bioactivity for mouse natural killer (NK) T cells to produce cytokines. RCAI-8, 9, 51, and 52 are the analogues with a pyrrolidine ring, and RCAI-18, 19, 49, and 50 are those with an azetidine ring. RCAI-18 was shown to be a potent inducer of cytokine production by mouse NKT cells, while RCAI-51 was a moderately active inducer.     

New carbocyclic nucleoside analogues with a bicyclo[2.2.1]heptane fragment as sugar moiety; Synthesis,X-ray crystallography and anticancer activity

An amine group was synthesized starting from an optically active bicyclo[2.2.1]heptane compound, which was then used to build the 5 atoms ring of a key 6-chloropurine intermediate. This was then reacted with ammonia and selected amines obtaining new adenine- and 6-substituted adenine conformationally constrained carbocyclic nucleoside analogues with a bicyclo[2.2.1]heptane skeleton in the sugar moiety. X-ray crystallography confirmed an exo-coupling of base to the ring and a L configuration of the nucleoside analogues. The compounds were tested for anticancer activity.     

Correlation of hydrogen-bonding propensity and anticancer profile of tetrazole-tethered combretastatin analogues

A series of 1,5-disubstituted tetrazole-tethered combretastatin analogues with extended hydrogen-bond donors at the ortho-positions of the aryl A and B rings were developed and evaluated for their antitubulin and antiproliferative activity. We wanted to test whether intramolecular hydrogen-bonding used as a conformational locking element in these analogues would improve their activity. The correlation of crystal structures with the antitubulin and antiproliferative profiles of the modified analogues suggested that hydrogen-bond-mediated conformational control of the A ring is deleterious to the bioactivity. In contrast, although there was no clear evidence that intramolecular hydrogen bonding to the B ring enhanced activity, we found that increased substitution on the B ring had a positive effect on antitubulin and antiproliferative activity. Among the various analogues synthesized, compounds 5d and 5e, having hydrogen-bonding donor groups at the ortho and meta-positions on the 4-methoxy phenyl B ring, are strong inhibitors of tubulin polymerization and antiproliferative agents having IC₅₀ value in micromolar concentrations.     

Syntheses of cellotriose and cellotetraose analogues as transition state mimics for mechanistic studies of cellulases

Cellotriose and cellotetraose analogues carrying cyclohexene rings were developed as molecular probes which are expected to mimic the transition state conformation of hydrolysis by cellulases. The cyclohexene ring was placed at the pyranose ring being expected to locate the -1 subsite of the enzyme. In order to evaluate these probes, sulfur derivatives of cellotriose and cellotetraose were also synthesized as the enzyme tolerant analogues which mimic the stable conformations of the natural cellulose. The binding assays using differential scanning calorimetry revealed that introduction of the cyclohexene ring is effective to the complexation with an endoglucanase, NCE5 from Humicola insolens.     

Purification, properties, and function of flavokinase from rat intestinal mucosa

Flavokinase (ATP:riboflavin 5'-phosphotransferase) [EC 2.7.1.26] was purified to apparent homogeneity from rat intestinal mucosa by fractionation with ammonium sulfate, gel filtration, and flavin affinity chromatography. The addition of ATP to the enzyme solution was necessary for its binding to the affinity gel. The apparent molecular weight of the enzyme was estimated to be 13,500 by gel filtration on Sephadex G-100 and by SDS-PAGE. The properties of the enzyme, including its flavin specificity, were studied. Three types of riboflavin analogues were used for the flavin specificity study; namely, ones modified at the ribityl group, and at positions 3 and 8 of the isoalloxazine ring. Of the analogues modified at the ribityl group or position 3 of the isoalloxazine ring, only 2'-deoxyriboflavin was phosphorylated and then only weakly. On the other hand, most analogues modified at position 8 of the isoalloxazine ring were good substrates for the kinase, an appropriate increase in the substituent volume at position 8 of the isoalloxazine ring resulting in an increase in the Vmax value. In a previous paper on the mechanism of intestinal absorption of riboflavin, we proposed that one of the specific processes for the absorption of riboflavin is phosphorylation by flavokinase [Kasai, S. et al. (1988) J. Nutr. Sci. Vitaminol. 34, 265-280]. The present results support this conclusion because analogues that were absorbed at low concentrations through a process specific for riboflavin in our previous study were phosphorylated effectively by the enzyme, whereas those that were absorbed solely through simple diffusion at all concentrations were not phosphorylated or only phosphorylated weakly. The properties of the flavokinases from intestinal mucosa and liver were compared.     

Conformationally restrained cyclic peptides as antagonists of luteinizing hormone-releasing hormone

Using minimum energy calculations and molecular dynamics techniques the preferred conformational states of LHRH and its analogues have been reported to involve a modified beta-bend between residues 5 to 8. Based on some of these models cyclic peptide analogues of LHRH antagonists were synthesised using solid phase peptide synthesis methodology. The analogues were tested for their ability to inhibit ovulation in normal cycling rats. Some analogues were also tested in receptor binding and in vitro LH release assays. The most potent cyclic peptide analogue, Ac-D-Phe(p-C1)-D-Phe(p-C1)-D-Trp-Ser-Glu-D-Arg-Leu-Lys-Pro-D-Ala-NH2 (V), had an ED50 value of 91.9 micrograms/kg in the inhibition of ovulation test. The corresponding linear peptide (IV) was about three times less potent. Analogues with smaller or larger ring sizes or with modifications within the ring were also prepared but these were either less potent or inactive, up to a dose of 1000 micrograms/kg, in inhibiting ovulation in normal cycling rats.     

Structure-Activity Relationships of Vasopressin Analogues on Release of Factor Viii in Dogs

Abstract

In order to study structure-activity relationships as to Factor VIII release conscious dogs were injected with analogues of vasopressin. The peptides used were chemically modified either in the hexapeptide ring structure of the vasopressin molecule or in the C-terminal tripeptide or in both. The results showed that an intact C-terminal appears to be of importance for retaining Factor VIII releasing activity of the analogues, whereas at least some modifications of the ring structure are tolerated without loss of activity. Decreased activity was also observed when the disulphide bridge was substituted with a monocarba bond.     

青蒿素及其类似物抗疟构效关系的DFT研究

为了从原子水平上揭示青蒿素及其类似物的结构与抗疟活性之间的关系,运用密度泛函理论DFT方法,在B3LYP/6-31G*水平上对青蒿素及其类似物二氢青蒿素、蒿甲醚和青蒿琥酯的结构和性质进行了理论计算。从分子的平衡构型、Wiberg键级、溶剂化能、偶极矩和静电势等方面分析了青蒿素及其类似物的抗疟构效关系。结果表明,青蒿素及其类似物结构中七元环上的过氧桥键、醚氧键以及六元环上的内酯结构是其抗疟作用的关键活性位,过氧桥键处负的静电势越多,青蒿素与血红素的相互作用越强,分子的抗疟活性越强。理论预测四个药物分子的抗疟活性顺序为:青蒿素<二氢青蒿素<蒿甲醚<青蒿琥酯,与实验活性结果一致。     

Synthesis and properties of photoaffinity labels for the pyridine dinucleotide binding site of NAD glycohydrolase.

Two new photoactive analogues of oxidized nicotinamide adenine dinucleotide (NAD+) which are resistant to cleavage by NAD glycohydrolase were synthesized and characterized. The beta-D-ribonucleotide ring of the nicotinamide riboside moiety of NAD+ was replaced with a 2,3-dihydroxycyclopentane ring forming a carbocyclic dinucleotide analogue. Photoreactivity was achieved by the incorporation of an azido group at the 8-position of the adenosyl ring. The previously published synthesis of carbocyclic pyridine dinucleotide analogues [Slama, J. T., & Simmons, A. M. (1988) Biochemistry 27, 183] was modified by resolving the carbocyclic 1-aminoribose analogues and producing optically pure (+)-(1S)- or (-)-(1R)-4 beta-amino-2 alpha,3 alpha-dihydroxy-1 beta-cyclopentanemethanol. Each of these was converted to the corresponding carbocyclic nicotinamide 5'-nucleotide analogue and coupled with 8-azidoadenosine 5'-monophosphate. Two photoactive and isomeric NAD+ analogues were thus prepared. 8-Azidoadenosyl carba-NAD is the analogue in which D-dihydroxycyclopentane is substituted for the D-ribose of the nicotinamide nucleoside moiety. 8-Azido-adenosyl pseudocarba-NAD contains the L-carbocycle in place of the D-ribotide ring. 8-Azidoadenosyl carba-NAD was shown to inhibit the NAD glycohydrolase from Bungarus fasciatus venom competitively with an inhibitor dissociation constant of 187 microM. 8-Azidoadenosyl pseudocarba-NAD was shown to inhibit the same enzyme competitively with a Ki of 73 microM. The superior NADase inhibitor, 8-azidoadenosyl pseudocarba-NAD, was characterized kinetically and shown to fulfill the criteria required of a specific active site directed photoaffinity probe. Irradiation of mixtures of the photoprobe and NAD glycohydrolase with short-wave ultraviolet light resulted in the rapid and irreversible loss of enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Novel 4-azasteroidal N-glycoside analogues bearing sugar-like D ring: synthesis and anticancer activities

A series of novel N-glycoside analogues with 4-azasteroid moiety bearing sugar-like D ring were conveniently synthesized by constructing the core dihydropyran ring embedded in 4-azasteroidal skeleton which was prepared from 4-aza-5α-androst-3,17-dione 1 in four steps. The structure of 6b were unambiguously proved by the appropriate X-ray structural analysis. Anticancer activity was found for all of the analogues with purinyl moiety against breast cancer (MCF-7), human neuroblastoma (SK-N-SH), cervical cancer cell (HeLa) and prostatic cancer (PC-3), while the analogue 7 containing 1,2,4-triazole heterocycle as the nucleobase was inactive against all of the tested cancer cell lines. The biology results showed the purinyl moiety attached to the pyran ring of 6a-d, substituent at 6'-position of purine base and introduction of a halogen atom at 2'-position of 6'-chloropurine had obviously effect on the evaluated anticancer activity.     

Adenosine deaminase prefers a distinct sugar ring conformation for binding and catalysis: kinetic and structural studies

Several recent X-ray crystal structures of adenosine deaminase (ADA) in complex with various adenosine surrogates have illustrated the preferred mode of substrate binding for this enzyme. To define more specific structural details of substrate preferences for binding and catalysis, we have studied the ADA binding efficiencies and deamination kinetics of several synthetic adenosine analogues in which the furanosyl ring is biased toward a particular conformation. NMR solution studies and pseudorotational analyses were used to ascertain the preferred furanose ring puckers (P, nu(MAX)) and rotamer distributions (chi and gamma) of the nucleoside analogues. It was shown that derivatives which are biased toward a "Northern" (3'-endo, N) sugar ring pucker were deaminated up to 65-fold faster and bound more tightly to the enzyme than those that preferred a "Southern" (2'-endo, S) conformation. This behavior, however, could be modulated by other structural factors. Similarly, purine riboside inhibitors of ADA that prefer the N hemisphere were more potent inhibitors than S analogues. These binding propensities were corroborated by detailed molecular modeling studies. Docking of both N- and S-type analogues into the ADA crystal structure coordinates showed that N-type substrates formed a stable complex with ADA, whereas for S-type substrates, it was necessary for the sugar pucker to adjust to a 3'-endo (N-type) conformation to remain in the ADA substrate binding site. These data outline the intricate structural details for optimum binding in the catalytic cleft of ADA.     

Quantitative assessment of mRNA cap analogues as inhibitors of in vitro translation.

Fifty-eight analogues of the 5'-terminal 7-methylguanosine-containing cap of eukaryotic messenger RNA were synthesized and tested for their ability to inhibit in vitro protein synthesis. A new algorithm was developed for extracting KI, the dissociation constant for the cap analogue.eIF4E complex, from protein synthesis data. The results indicated that addition of a methyl group to the N2 of guanine produced more inhibitory compounds, but addition of a second methyl group to N2 decreased the level of inhibition dramatically. Aryl substitution at N7 improved the efficacy of guanine nucleoside monophosphate analogues. Substitution of the aromatic ring at the para position with methyl or NO2 groups abolished this effect, but substitution with Cl or F enhanced it. By contrast, aryl substitution at N7 in nucleoside di- or triphosphate analogues produced only minor effects, both positive and negative. By far the strongest determinants of inhibitory activity for cap analogues were phosphate residues. The beneficial effect of more phosphate residues was related more to anionic charge than to the number of phosphate groups per se. The second nucleotide residue in analogues of the form m7GpppN affected inhibitory activity in the order G > C > U > A, but there was no effect of 2'-O-modification. Opening the first ribose ring of m7GpppG analogues dramatically decreased activity, but alterations at the 2'-position of this ribose had no effect. Non-nucleotide-based cap analogues containing benzimidazole derivatives were inhibitory, though less so than those containing 7-methylguanine.     

Synthesis and SAR exploration of dinapsoline analogues

Dinapsoline is a full D(1) dopamine receptor agonist that produces robust rotational activity in the unilateral 6-OHDA rat model. This compound is orally active, and shows a low tendency to cause tolerance in rat models. The active enantiomer was determined to have the S-(+) configuration, and the opposite enantiomer is essentially devoid of biological activity. Taken together, dinapsoline has significant metabolic and pharmacological advantages over previous D(1) agonists. In an attempt to define the structure-activity relationships (SARs) and to map out the key elements surrounding the unique structure of dinapsoline, core analogues and substitution analogues of the parent tetracyclic condensed ring structure were prepared. Based on a recently developed synthesis of dinapsoline and its enantiomers, both core and substitution analogues on all four rings (A, B', C and D ring) of dinapsoline were synthesized. It was found that affinity for both D(1)and D(2) receptors was decreased by most substituents on the A, B', and C rings, whereas D ring substitutions preserved much of the dopamine receptor binding activity.     

Thrombomodulin induction in cultured human endothelial cells by 9-cis-locked retinoic acid analogues

9-cis-Retinoic acid (RA) analogues devised to lock the 9-cis double bond by ring formation were synthesized using two stereoselective carbon-carbon bond formation reactions as key steps. The palladium-mediated Suzuki reaction was adopted to construct a 7E-double bond (RA numbering) and the Horner-Emmons olefination was employed for stereoselective 11E-double bond (RA numbering) formation. The synthesized 9-cis-RA analogues that are locked by five-membered ring systems (cyclopentene, dihydrofuran, and dihydrothiophene) were shown to have comparable thrombomodulin induction activities to that of 9-cis RA. Conformational analysis of these compounds showed their similarity to 9-cis RA in the spatial orientation of the side chain and the terminal carboxy group.     

Mechanism of colchicine binding to tubulin. Tolerance of substituents in ring C' of biphenyl analogues

The limits of structural variation of the substituent in position 4' of ring C' of biphenyl colchicine analogues (ring C in colchicine) were probed by the synthesis of a number of analogues and the examination of their binding to tubulin and its consequences. Binding was found to require the location in three-dimensional space of the oxygen in the 4'-substituent at a locus not far distant from those of the colchicine ring C oxygens. All those analogues that bind to the colchicine site of tubulin induced the GTPase activity and inhibited microtubule assembly, those containing a carbonyl group substoichiometrically and the others stoichiometrically. A similar relation was found for the induction of the abnormal polymerization of the colchicine analogue-tubulin complex, with methoxy-containing compounds requiring a higher temperature to induce the polymerization. A concerted analysis of the binding thermodynamics of colchicine and its various analogues has shown full consistency with the previously proposed two-step binding pathway that involves two nonidentical binding moieties in the ligand [Andreu, J. M., & Timasheff, S. N. (1982) Biochemistry 21, 534-543]. Comparison of the binding parameters of colchicine, its des(ring B) analogue (MTC), and ring A and C compounds individually with the thermodynamic parameters deduced for the first steps of the bindings of colchicine and MTC [Engelborghs, Y., & Fitzgerald, T. J. (1987) J. Biol. Chem. 262, 5204-5209] have led to the conclusion that binding can occur by two pathways leading to the identical product. In the first pathway, ring A binds first; this is followed by a rate-determining thermodynamically indifferent reaction (protein conformation change), and finally a rapid binding of ring C. In the second pathway, the events are the same except that the order of binding of the rings is reversed. Colchicine, due to the steric hindrance of ring B, can follow only the second pathway. For MTC, both kinetic pathways are open and binding may be initiated by random first contact of either ring A or ring C.     

Synthesis of imidazole-containing analogues of farnesyl pyrophosphate and evaluation of their biological activity on protein farnesyltransferase

With the aim of creating new bisubstrate inhibitors of protein farnesyltransferase (FTase), new carboxylic farnesyl pyrophosphate analogues have been designed and synthesized. The original structures are built around three elements: a prenyl moiety, a 1,4-diacid motif and an imidazole ring. All the compounds were evaluated for their ability to inhibit FTase and compared with the corresponding derivatives lacking the imidazole ring, synthesized for that purpose. These new compounds are not bisubstrate inhibitors probably because the imidazole ring is not in the right position to interact with the zinc atom. However these derivatives display FPP competitive inhibition with a good activity in the carboxylic farnesyl pyrophosphate analogues series.     

Analysis of stereoelectronic properties of camptothecin analogues in relation to biological activity

Camptothecin and four of its 10,11-methylenedioxy analogues were examined for their activity against the pathogenic protozoan Leishmania donovani in vitro. The methylenedioxy analogues were 36- to 180-fold more potent than the parent camptothecin, possessing IC50 values ranging from 160 to 32 nM against the parasite. Our finding that the methylenedioxy camptothecins possess greater activity than camptothecin, which is also the case for other cell types and for the generation of cleavable complex in the presence of DNA and purified mammalian topoisomerase I, prompted us to examine the molecular features of camptothecin and methylenedioxy camptothecin analogues. A delocalization of positive potential was observed in the methylenedioxy camptothecin analogues, which could increase the affinity of these molecules for DNA. In addition, geometrical and electronic differences between the E ring of camptothecin and its methylenedioxy analogues were noted. One or both of these factors may contribute to the superior biological activity of the methylenedioxy camptothecin analogues.