WO1996009326A1

WO1996009326A1 - Reversible and controllable closing and opening of the guest-binding cavity of cyclodextrin derivatives and related host molecules

Info

Publication number: WO1996009326A1
Application number: PCT/US1995/011883
Authority: WO
Inventors: Rina Arad-Yellin; Bernard S. Green
Original assignee: Yissum Research Development Company Of The Hebrew University Of Jerusalem
Priority date: 1994-09-19
Filing date: 1995-09-18
Publication date: 1996-03-28
Also published as: IL115355A0; AU3592195A

Abstract

A method for trapping a guest in and releasing the guest from the interior of a cyclic compound, which includes the steps of first contacting the cyclic compound and the guest so as to allow the guest to enter the interior of the cyclic compound, then activating the cyclic compound to bring about the entrapment of the guest in the interior of the cyclic compound. Subsequently, the cyclic compound is further activated to release the guest from the interior of the cyclic compounds. The cyclic compound includes a cyclic structure and one or more substituents which are chemically bonded to the cyclic structure and which, upon activation, react with the cyclic structure or with another substituent to form a bridge which at least partially blocks access to the interior of the cyclic compound. Upon further activation, the bridge opens to unblock access to the interior of the cyclic compound, thereby releasing the guest.

Description

REVERSIBLE AND CONTROLLABLE CLOSING AND OPENING

OF THE GUEST-BINDING CAVITY OF CYCLODEXTRIN

DERIVATIVES AND RELATED HOST MOLECULES

FIELD AND BACKGROUND OF THE INVENTION The present invention relates to the reversible and controllable closing and opening of a cavity in certain cyclic compounds, such as cyclodextrins and their derivatives, possessing a cavity of a size and shape capable of including a non-covalently bound guest molecule or other material (hereinafter referred to as "guest"), so as to alternately trap and release, one or more guests.

In a variety of applications, it is desirable to be able to deliver one or more molecules to a specific location while shielding the molecule from adverse conditions prior to its reaching its destination or to permanently shield or encapsulate the molecule so as to prevent it from adversely affecting its surroundings or from being affected by its surroundings. One important example of the former application, involving the reversible locking of a guest in a host, is in the delivery of a drug to a specific tissue. It is often the case that a significant amount of drugs which are intended for a specific tissue reacts with other tissues and never reach their intended destination. To compensate for this effect, such drugs are administered in doses which are sufficiently high to ensure that an adequate amount of the drugs will reach its destination. The result is a massive systemic application of the drug to a variety of non-intended tissues which could lead to various adverse side-effects and which increase the cost of the effective dose. An example of the latter applications, calling for the irreversible locking of the guest within the host, may be the encapsulation of a harmful molecule so as to prevent the possibility of its detrimental interaction with its surroundings. In a third category of applications it may be desired to partially lock a guest within a host in such a way that the guest is spontaneously released over a significant amount of time. Such applications may be useful in the delivery of small amounts of medications over an extended periods of time. Such trapping and controlled or slow release could be useful for stabilization, solubilization, and/or delivery of a taste or odor substance, a medication, a pesticide, a pheromone, and the like.

5 Cyclodextrins (also referred to hereinafter as "CDs") and modified cyclodextrins have been widely studied because of their ability to reversibly bind, and often modify, the properties of guest molecules in their torus-shaped cavities. See, for example, J. Szejtli, Cyclodextrins and Their Inclusion Complexes, Academiai Kiado, Budapest (1982), Carbohydr. Res.

10 192, 1-370 (1989) and Bender, M.L. & Komiyama, M. Cyclodextrin Chemistry (Springer, Berlin, 1978), incorporated by reference in their entirely as if fully set forth herein.

Cyclodextrins have also played a prime role in the design of many useful materials and devices. See, for example, Duchene, D. (Ed.), New

15 Trends in Cyclodextrins and Derivatives (Editions de Sante, Paris, 1991), which is incorporated by reference in its entirety as if fully set forth herein.

A shortcoming of the earlier work is that the binding of a given guest and CD, or CD derivative, is not easily predictable or controllable.

In many cases, the CD and guest form weak complexes which can be

20 detected but which cannot be isolated. See, for example, Bender, M.L. and Komiyama, M., Cyclodextrin Chemistry (Springer, Berlin, 1978), which is incorporated by reference in its entirety as if fully set forth herein.

Cyclodextrins and their derivatives are particularly attractive for application in trapping a guest since they are relatively inexpensive, easy

25 to obtain, their syntheses are well-described in the literature, they are non- toxic and environmentally benign.

There is thus a widely recognized need for, and it would be highly advantageous to have systems, including cyclodextrin compounds, i.e., CD derivatives, which will make it possible to tightly hold a guest and which

30 preferably further allows for the precise control of the subsequent release of the guest. There is additionally a need for complexes which include a cyclodextrin derivative an entrapped guest which is preferably releasable.

SUMMARY OF THE INVENTION

According to the present invention there is provided a substituted cyclic compound useful in the entrapment of a guest, comprising: (a) a cyclic structure having a cavity possessing a size and shape to include a non-covalently bound guest molecule; and (b) at least one substituent chemically bonded to the cyclic structure, the substituent, upon activation, reacting with the cyclic structure or with another substituent to form a bridge which at least partially blocks access to the cavity of the cyclic structure.

Also according to the present invention, there is provided a complex, comprising (a) a substituted cyclic compound useful in the reversible entrapment of a guest, including: (i) a cyclic structure having a cavity possessing a size and shape to include a non-covalently bound guest molecule; and (ii) at least one substituent chemically bonded to the cyclic structure, the substituent, upon activation, reacting with the cyclic structure or with another substituent to form a bridge which at least partially blocks access to the cavity of the cyclic structure; and (b) a guest molecule trapped within the cavity.

Further according to the present invention, there is provided a method for trapping a guest in, and releasing the guest from, the interior of a substituted cyclic compound, comprising the steps of: (a) contacting the substituted cyclic compound and the guest so as to allow the guest to enter the substituted cyclic compound; (b) activating the substituted cyclic compound to bring about the entrapment of the guest in the interior of the substituted cyclic compound; and (c) further activating the substituted cyclic compound to release the guest from the substituted cyclic compound; the substituted cyclic compound characterized in that it includes: (i) a cyclic structure having a cavity possessing a size and shape to include a non-covalently bound guest molecule; and (ii) at least one substituent chemically bonded to the cyclic structure, the substituent, upon activation, reacting with the cyclic structure or with another substituent to form a bridge which at least partially blocks access to the cavity of the cyclic structure.

According to further features in preferred embodiments of the invention described below, the substituted cyclic molecule is a cyclodextrin (α-, β-, γ- or δ-cyclodextrin) or cyclodextrin derivative such as commercially available sugar substituted cyclodextrins, methylated, hydroxyethylated or hydroxypropylated cyclodextrins, and the like. The substituted cyclic molecule may have some of the hydroxyl groups converted to amino or other functional groups. The substituted cyclic molecule may further be a synthesized cyclodextrin derivative having aryl, alkyl, or other substituents designed to enlarge or change the properties of the cyclodextrin. Further, the substituted cyclic molecule may be a synthetic sugar derivative such as the recently described cycloisomaltohexaoside (S. Houdier and P.J.A. Vottero, Angew. Chem. Int. Engl. 33, 354-6 (1994)) or cylindrical tubes of cyclodextrins such as that described recently (A. Harada, J. Li and M. Kamachi, Nature 364, 516-518 (1993)). The substituted cyclic molecule may be a cyclophane derivative (F.N. Dietrich, "Cyclophanes", Royal Society of Chemistry, Cambridge 1991) or calixarene derivative (CD. Gutsche, "Calixarenes", Royal Society of Chemistry, Cambridge, 1989).

The substituent may be a photoreactive group such as a cinnamate, a coumarin, a stilbene, an anthracene derivative, and the like. Mixtures of different substituents can be used as well, such as cinnamate and acrylate or crotonate. The photoreactive group may be an azide or diazoketone or other group which becomes activated (e.g., converts to nitrene or carbene upon photoactivation) and then reacts with a different substituent on the cyclic molecule. The substituents may contain the diene and the dieneophile components and the reaction which forms the bridge is the Diels-Alder reaction. The substituent may contain any of the commonly used chemical cross-linking functional groups which are used to covalently link two different groups, such as those described in K.K. Han, C. Richard and A. Delacourte, Int. J. Biochem. 16, 129-145 (1984), which are incorporated by reference as if fully set forth herein. The substituent may be a group which will result in a peptide-containing bridge, a phosphate- containing bridge, a phosphate-containing bridge, a disulfide-containing bridge, or related groups across the substituted cyclic molecule. The substituents may further contain additional groups in order to render them water soluble or amphiphilic, and the like. The substituents may contain additional groups, such as peptides, peptide-mimics, drugs or drug analogs, which have affinity for biological receptors, and the like. The reaction may also be a pH change which induces cleavage of a covalent bond.

According to still further features in the described preferred embodiments, the activation to trap the guest is thermal, chemical or photochemical, while the further activation to release the guest is thermal, chemical, photochemical or enzymatic.

The cavities of the cyclic molecules employed in this invention may have a tunnel-like shape, i.e., open on two or more sides or ends, or they may have a concave shape that is open on one side or end only. Examples of cavities which are open on two ends are provided by the cyclodextrins and the crown ethers. Examples of cavities which are open on one side only are provided by the calixarenes and hemicarcerands. Examples of tunnel-like activities that have openings on three or more sides are provided by zeolites such as zeolite X and zeolite ZSM-5. For cavities possessing more than one opening, the openings may be of the same or different size, but at least one of the openings should be of sufficient size to permit passage of a guest molecule into the cavity.

The cyclic molecules useful in this invention may possess any number of substituents, which are oriented around or above any opening or openings of the cavity so as to at least partially block or close the opening when the substituents are activated. In this way, the cavity is partially or completely blocked when the substituents are activated and the guest molecule is trapped inside.

The cavity of the cyclic molecule may possess a favorable non- covalent bonding interaction with the guest molecule, e.g., a van der Waals, dispersion, dipolar, ionic or hydrogen bonding interaction. Alternatively, the cavity may interact only weakly, not at all, or even unfavorably with the guest molecule. In this case, the guest is introduced into the cavity by a mass action (concentration) effect and is bound and trapped in the cavity solely by the physical blocking action provided by the cavity walls and by the bridges formed over the cavity when the substituents are activated. An advantage of the present invention is that it is useful for binding guests which, in the absence of the activatable substituents, would be included only to small extent in the cavity due to weak or unfavorable binding interactions.

The present invention successfully addresses the shortcomings of the presently known configurations by providing hosts, host/guest complexes and methods for creating host/guest complexes, for tightly holding a guest upon activation and, preferably, for controllably releasing the guest upon further activation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: FIG. 1 is a schematic view of the reversible inclusion and imprisonment of a guest molecule, G, in the interior of a cyclodextrin (CD) derivative and the subsequent entrapment and release of the guest molecule.

FIG. 2 shows a concrete example of the process depicted in Figure 1, using the intramolecular photocycloaddition reactions of percinnamoylated CDs.

FIG. 3 shows a number of infrared spectra as described below;

FIG. 4 shows a number of mass spectral analyses of β -CD-PC as described below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is of methods, and compounds useful in those methods, for reversibly and controllably trapping a guest in the interior of a cyclic compound, such as a CD derivative, which can be used in a variety of applications, including, but not limited to, the delivery of a drug to a specific body tissue.

For tissue-specific delivery of a guest, such as a drug, a cytotoxic substance, and the like, the bridge which locks in the guest includes a peptide, phosphate, disulfide or other functional group or molecular structure, which selectively reacts chemically, cleaving the bridge and releasing the guest, at the designated tissue as a result of enzymes or other molecules present at that tissue. In addition to tissue-specific delivery, use could be made of pathogen-specific delivery, so that the delivery occurs in the vicinity of a foreign tissue. The substituted cyclic molecule may be constructed such that the bridge includes a structure, such as a peptide, phosphate, disulfide, and the like, which is specifically recognized by an enzyme or receptor at the target tissue. Alternatively, one of the additional substituents is the tissue- or pathogen-directing function. As an example, a peptide bridge which contains a peptide which is recognized and reacts with HIV protease will be hydrolyzed by the AIDS virus and release an antiviral agent trapped in the CD close to the viral particle and allow higher local concentrations of the drug than is otherwise possible, which results in improved therapy and lessened exposure of healthy tissue to the drug. The principles and operation of the present invention may be better understood with reference to the drawings and the accompanying description.

Referring now to the drawings, Figure 1 illustrates the general approach to achieving controlled binding and release. The approach involves the use of suitable cyclic compounds made up of a cyclic structure and at least one substituent which is chemically bonded to the cyclic structure. Upon activation, the substituent reacts with the cyclic structure or with another substituent on the same cyclic structure to form a bridge which at least partially blocks access to the interior of the cyclic compound preventing a guest from leaving. Upon further activation, the bridge opens to unblock access to the interior of the cyclic compound releasing the guest.

Thus, as illustrated in Figure 1, the approach of the present invention to achieve the controlled binding and release of a guest and preferably involves the use of CDs modified with substituents which react to form bridges which trap guests. Subsequent guest release is accomplished by bridge opening through bond-breaking reactions. Thus, Figure 1 shows the reversible inclusion and imprisonment of guest molecule, G, by a cyclodextrin derivative and the subsequent closure of the top (primary, C-6, rim) and bottom (secondary, C-2,3, rim) of the CD derivative through the intramolecular chemical linking of the CD substituents, thereby trapping the guest. An appropriate, and different, chemical reaction opens the sealed CD derivative and releases the guest.

It is to be pointed out that the cavity need not have binding properties for the guest. Binding can be accomplished merely by exposing the host to a large excess of the guest and then carrying out the trapping reaction. This represents an important advantage over the prior CD art, in which the complexation occurs only if there is favorable binding interaction between the host cavity and the guest. A specific example of the scheme illustrated in Figure 1 is shown in Figure 2 which involves the intramolecular photocycloaddition reactions using percinnamoylated CDs.

Irradiation in the presence of a guest, using 300 nm light, leads to cyclobutane formation, the cyclobutanes constituting the bridges which lock in the guest. Acid-catalyzed ester exchange in methanol breaks the ester bonds of the bridge and releases the guest. The cyclobutane products shown in Figure 2 were obtained. Photocleavage, using 254 nm light, of the cyclobutane groups in the bridged product also releases the guest, G. Alternatively, an enzyme, such as esterase or lipase, can be used to catalyze hydrolysis of the ester bonds yielding the products shown in Figure 2, as carboxylic acids, and releasing the guest. The depicted cage photoproduct represents an ensemble of structures containing varying numbers of cyclobutane rings and cis- and trans-cinnamate residues.

EXAMPLE 1: Synthesis and structural characterization of the CD cinnamate host

All of the hydroxyl groups in α-cyclodextrin (α-CD) and β-CD were esterified with cinnamic acid residues in order to obtain suitable derivatives for closing the top (primary hydroxyl) and bottom (secondary hydroxyl) openings of CDs and imprisoning guest molecules present during the closure reaction. α-Cyclodextrin per-cinnamate (α-CD-PC) and β -CD-PC were obtained by treating the CD with excess cinnamoyl chloride in pyridine (see, Ellwood, P., Spencer, CM., Spencer, N., Stoddart, J.F. & Zarzycki, R. J. Inc Phenom. 12, 121-150 (1992), which is incorporated by reference in its entirety as if fully set forth herein). The purified (column chromatography on silica gel) products were isolated as microcrystalline solids having 'H and ¹³C NMR spectra in full accord with peracylated (6- and 7-fold, respectively) time-averaged symmetrical structures (three non-equivalent cinnamate signals). Mass spectral analysis (FAB) afforded the expected protonoated molecular ions, MH\ values. The percinnamates are soluble in organic solvents such as chloroform, methylene chloride, acetone, acetonitrile, and DMF but insoluble in water, protic (methanol, ethanol, 1- and 2-propanol) or hydrocarbon (n-hexane, n-octane, isooctane) solvents.

EXAMPLE 2: General experimental and analytic method

When deaerated solutions of α-CD-PC or β -CD-PC were irradiated (Pyrex-filtered light from a Xenon-Mercury lamp), the 276 nm absorption due to the cinnamoyl chromophore (Ph-CH=CH-CO-) diminished with time and the IR bands at 1721 and 1636 cm^"1 (CO and CH=CH, respectively) were replaced by a new band at 1752±1 cm ¹, expected for the aliphatic ester C=0 present in the cyclobutane (truxinate) photoproducts. For preparative reactions, deaerated solutions were irradiated in a Rayonet Reactor fitted with lamps having strong emission at ca. 300 nm. A number of solvents which are potential CD guests were used; irradiated solutions of ethyl acetate and N-methylpyrrolidin-2-one (NMP) were studied in more detail.

After irradiation (ca. 120 hrs), the cyclodextrin-containing material was isolated by evaporation of the solvent (ethyl acetate) or by precipitation with methanol (NMP). The solids were redissolved in methylene chloride and precipitated with methanol. Centrifugation and removal of supernatant left solids which were triturated with methanol and centrifuged again. Finally, the solid products were warmed to ca. 100°C for 1 hr (1 mm Hg).

Because of the dilute conditions used (1-5 x lO^M), the photochemical reactions of the percinnamoylated CDs, are believed to be largely, if not exclusively, intramolecular, (see, Green, B.S., Rabinsohn, Y. & Rejto, M. Carbohyd. Res. 45, 115-126 (1975), which is incorporated by reference in its entirety as if fully set forth herein). Thin layer chromatography corroborates this showing very similar Rf mobility values for the unirradiated and irradiated samples. When a purified, irradiated β -CD-PC sample was treated with methanol/HCl to effect ester exchange, methyl cinnamate (cis- and trans-isomers) and dimethyl esters of cinnamate photodimers were obtained (Figure 1). The major dimers are β- and δ-truxinate (1:4, ca. 90% of the total; identified by GLC comparison with authentic samples and NMR of the purified reaction mixture) as well as other truxinates which appear to be the product of cis + trans photoaddition. The ratio of photodimer to cinnamate and the decrease of the cinnamate UV absorption indicate that ca. 80% of the cinnamates have reacted under the conditions used.

EXAMPLE 3: Control experiment without irradiation and trapping Unirradiated α-CD-PC or β -CD-PC was dissolved in NMP and methanol added to precipitate the CD-PC; the solids were dissolved in methylene chloride and precipitated again with methanol. After the solids were warmed to about 100°C for 1 hr (1mm Hg), the characteristic IR band of NMP (e.g., 1676 cm^"1) was absent from the samples (Figure 3 A). Similarly, when the product from an irradiated ethyl acetate solution of α-CD-PC or β -CD-PC was dissolved in NMP and purified according to this same protocol, the product contained no NMP (IR, Figure 3D). EXAMPLE 4: Experiments illustrating trapping and release

FIG. 3 shows infrared spectra, taken with a Nicolet 510 FT-IR spectrometer using KBr pellets, of: (A) β-CD-PC, before irradiation; (B) β-CD-PC, after irradiation in ethyl acetate and wor up as described below. The bands at 1636 and 1721cm^"1, associated with the CH=CH and C=0 absorption of the cinnamate, have decreased and a new band at 1750 cm^"1 appears; (C) sample B after dissolving in NMP and reisolation without heating in vacuum (traces of NMP are present, as shown by band at 1684 cm^'1); (D) same as sample C but heated for 1 hr at 100°C at a pressure of 1 mm Hg; no trace of NMP is indicated but the bands at 1742 (ethyl acetate C=0) and 1750 cm' here and in spectrum C are unchanged; (E) β-CD-PC, after irradiation in NMP and workup as described in text; the strong band at 1684 cm^'1 indicates trapped NMP; (F) same as sample E, but heated for 2 hr at 200°C at a pressure of 1mm Hg; no change from E is noted; (G) sample as in E after dissolution in ethyl acetate, irradiation in a quartz tube (254 nm wavelength light; 120 hrs) and workup as before; this spectrum was recorded in chloroform and indicates complete release of guest upon irradiation.

The C=0 band (1684 cm^'1) in the IR spectra of complexed NMP in the "locked" CD cage is shifted relative to uncomplexed NMP (1676 cm^"1); this is observed in both solution (chloroform) and solid matrices (KBr) and is consistent with a guest restricted to the less polar environment of the CD interior where hydrogen-bonding is less favorable.

Further evidence for guest entrapment in a closed CD cavity was obtained by mass spectral analysis of the samples before and after irradiation as a function of sample warming.

Figure 4 shows the results of mass spectral analyses of β-CD-PC (A) before and (B) after irradiation in NMP. The insert probe of a PGS-70B Finnigan-Mat instrument was kept at room temperature for 60 sec and then heated to 400°C over a period of 120 sees. Spectra were recorded at 1.5 sec intervals. Both total ion and prominent guest ions (m/e 100, MH⁺ for NMP; for ethyl acetate, data not shown: m/e 88) were monitored.

In Figure 4A nearly all of the ions appear at room temperature and at the early stages of warming; these are due to the adsorbed or included NMP in this sample which was dried in vacuum at room temperature but not heated. It is to be noted that D is the composite of spectra 17-24 from sample A and is the same as C, the spectrum of authentic NMP, taken under identical conditions. The peak at ca. spectrum no. 125 (ca. 375°C) is believed to be due to disintegration of β-CD-PC. The small peak in the m/z 100 monitored spectrum, at spectrum no. 125, is due to traces of NMP and other species. Assuming identical sample conditions, this peak is <5% of the NMP peak in B.

In Figure 4B nearly all of the ions appear at ca. 375°C (spectrum no. 120 corresponds to this temperature); E is the spectrum of the released molecules (combined spectra 118-121 of sample B; spectra 94-107 were subtracted to eliminate noise) and is seen to be NMP; the combined spectra 121-128 contain NMP and other ions ascribed to disintegration of β- CD-PC For all of the guests studied, the thermal release, as detected by appearance of the guest signals in the mass spectrum, only takes place when the complex is heated to ca. 350°C By contrast, adsorbed guest or guest included in unirradiated CD-PC is released directly at room temperature (Figure 4A).

Irradiation of closed β-CD-PC NMP complex in ethyl acetate or in acetonitrile at a wavelength (254 nm) which is known to photochemically split aryl cyclobutane rings (see, Rennert, J. & Grossman, D. J. Photochem. 3, 163-174 (1974), which is incorporated by reference in its entirety as if fully set forth herein) followed by precipitation with methanol and the standard work up, afforded product lacking the characteristic guest NMP IR band at 1684 cm^"1 (Figure 3G). Thus, the sealed CD cavity may be opened, and the guest released, by irradiation with low wavelength light.

Many CD-PC conformations may possess the close cinnamate- cinnamate contacts required for 2+2 phtocycloaddition reactions; their photoproducts cannot be formulated by a single structure since they are ensembles of may isomeric molecules. Cinnamate residues on both the primary (C-6) rim and the secondary (C-2,3) rim of the CD cavity may react. Most preferably in the practice of the present invention, substituents on both the primary and the secondary rim react, thereby forming bridges which block both sides of the CD cavity and prevent release of the trapped guest. In addition to the CD-percinnamate described in the examples, CD cinnamates having a lower degree of substitution (e.g., 2-7 cinnamates on the primary rim and 2-14 cinnamates on the secondary rim of the β-CD cavity) are useful for trapping guests according to the present invention. Bridging across cyclodextrins and other host molecules has been studied by a number of researchers (see, Breslow, R., Czarniecki, M.F.,

Emert, J. and Hamaguchi, H.J., Amer. Chem. Soc. 102, 762-770 (1980);

Tabushi, I., Shimokawa, K., Shimizu, N., Shirakata, H. and Fujita, K.J.,

Chem. Soc. 98, 7855-7856 (1976), which are incorporated by reference in their entirety as if fully set forth herein) but the formation of closed-surface hosts via intramolecular reactions has not been previously described. There is much interest in on-off switching of chemical (see, Vogtle, F.

Supramolecular Chemistry, J. Wiley, Chichester 1991, which is incorporated by reference in its entirety as if fully set forth herein) or biological activity (see, Tawfik, D.S., Chap, R., Eshhar, Z. & Green, B.S.

Protein Engineering 7, 431-434 (1994), which is incorporated by reference in its entirety as if fully set forth herein) and particularly photochemical on-off triggering of properties (see, Bioorganic Photochemistry Volume 2:

Biological Applications of Photochemical Switches, Edited by H. Morrison, John Wiley & Sons, Inc., New York 1993, which is incorporated by reference in its entirety as if fully set forth herein). The cyclodextrin percinnamates, related to other acylated CDs, (see, Canceill, J., Jullien, L, Lacombe, L. & Lehn, J.-M. Helv. Chim. Acta 75, 791-812 (1992) and references cited therein, which is incorporated by reference in its entirety as if fully set forth herein) provide an especially facile entry to closed-surface cavities, termed carceplexes (see, Robbins, T.A., Knobler, C.B., Bellew, R.B., & Cram, D.J. J.Am. Chem. Soc. 116, 111-122 (1994) and references cited therein; Cram, D.J. Nature 356, 29-36 (1992), which are incorporated by reference in their entirety as if fully set forth herein) and to switchable states using photochemical reactions. Non-photochemical intramolecular closure is an important extension of the scheme depicted in Figure 1.

Depending on the volume of the enclosed CD cavity and the geometries and volumes of the guests, more than one guest, of the same or different nature, may be encapsulated and otherwise unattainable guest-guest interactions, and chemical transformations, may thus become possible (IR data indicate that the cage products of irradiated β-CD-PC in NMP contain more than one NMP molecule). γ-CD-PC is more versatile for this application; furthermore, substituents which extend the cage sizes may be envisaged for the design of different cavity shapes and sizes. By suitable choice of the chromophore (substituted cinnamates, etc.) the wavelength of opening and closing of the CD-cages can be controlled. Indeed, many different closing functionalities may be considered, for reversible (or irreversible) opening, and for tailored applications, such as the incorporation of enzyme-selective bridges for tissue-specific targeting and release of drugs. EXAMPLE 5: Additional experiments describing peptide-bridged cavities

α>, β-, γ-cyclodextrin was converted using methods found in the literature to partially or fully substituted substances where the primary hydroxyl group has bulky groups such as tert-butyl, trityl, and the like. These substances were then treated with a dipeptide, tripeptide, tetrapeptide in which the N-terminal position is a chloroacetyl group (or other appropriate reactive group which will result in an ether covalent bond with the CD-secondary OH groups). The carboxyl group of the peptide, suitably protected during the first step, if necessary, was then activated, as by DCC or EDC, in order to react with one of the secondary CD-secondary OH groups to form an ester bond and complete the bridge which closes or partially closes the CD cavity. Depending on the guest used or preferences of the experimenter, both the ether-forming and ester-forming reactions can be carried out in the presence of the guest to be entrapped. Alternatively, the ether-forming reaction can be carried out first, in the absence of the guest, and then, in the presence of the guest, the ester-forming linkage was made. One or more such bridges were formed, depending on the guest. The cavity was opened by a chemical hydrolysis at the ester linkage or by an enzyme-catalyzed hydrolysis at the ester or peptide bond.

EXAMPLE 6: Additional experiments describing photo-closure using coumarins and subsequent photochemical, thermal, chemical and enzymatic guest release

Umbelliferone (7-hydroxycoumarin) was converted to the chloroformate or to the chloroacetyl analog. These substances were then used to fully or partially react with the hydroxyl groups on a CD derivative. The resulting polycoumarin derivative can be used analogously to the percinnamates discussed above, to trap guest substances using photochemical reactions. The photocycloaddition of coumarins and the chemistry of the coumarin photodimers has been extensively studied and can be directly used for the purpose of this invention. See, for example, M. Hasegawa and K. Saigo, in Volume 2 of Photochemistry and Photophysics, Chapter 2, "Synthesis and properties of polymers having coumarin dimer moieties", CRC Press, Boca Raton, Florida, pp. 27-56, which is incoroprated by reference as if fully set forth herein.) Thus, β-CD is peracylated with the chloroformate or the chloroacetyl derivative of umbelliferone. The resulting substance is dissolved in a solvent containing the guest or the guest itself. Using NMP as guest, a solution of the CD derivative was irradiated with light of 300 nm wavelength; the NMP was shown to be trapped inside the CD cavity by the same methods described for CD-PC NMP complexes. Release of the guest was effected in the following ways: irradiation with light of ca. 277 nm wavelength; heating the trapped complex to between 220 and 310°C; hydrolysis with low or high pH; ester exchange with methanol containing HCl; and treatment with an enzyme, such as esterase or lipase.

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.

Claims

WHAT IS CLAIMED IS:

1. A substituted cyclic compound useful in the entrapment of a guest, comprising:

(a) a cyclic structure having a cavity possessing a size and shape to include a non-covalently bound guest molecule; and

(b) at least one substituent chemically bonded to said cyclic structure, said substituent, upon activation, reacting with said cyclic structure or with another substituent to form a bridge which at least partially blocks access to said cavity of said cyclic structure.

2. A substituted cyclic compound as in claim 1 , wherein said bridge, upon further activation, opens to unblock said access to the interior of the substituted cyclic compound.

3. A compound as in claim 1, wherein said cyclic structure is selected from the group consisting of α-cyclodextrin, β -cyclodextrin, γ- cyclodextrin, δ-cyclodextrin.

4. A compound as in claim 1, wherein said cyclic structure is β-cyclodextrin.

5. A compound as in claim 1, wherein said at least one substituent includes a photreactive group.

6. A compound as in claim 1, wherein said at least one substituent is selected from the group consisting of cinnamate, coumarin, stilbene, and anthracene. 19

7. A compound as in claim 1, wherein said at least one substituent is cinnamate.

8. A compound as in claim 4, wherein said at least one substituent is cinnamate.

9. A compound as in claim 1 , wherein said activation is thermal.

10. A compound as in claim 1, wherein said activation is chemical.

11. A compound as in claim 1, wherein said activation is photochemical.

12. A compound as in claim 1, wherein said further activation is thermal.

13. A compound as in claim 1, wherein said further activation is chemical.

14. A compound as in claim 1 , wherein said further activation is photochemical.

15. A compound as in claim 1, wherein said further activation is enzymatic.

16. A compound as in claim 1 , wherein at least one of said at least one substituents extends above said cyclic structure and at least one of said at least one substituents extends below said cyclic structure.

17. A method for trapping a guest in, and releasing the guest from, the interior of a substituted cyclic compound, comprising the steps of:

(a) contacting the substituted cyclic compound and the guest so as to allow the guest to enter the substituted cyclic compound;

(b) activating the substituted cyclic compound to bring about the entrapment of the guest in the interior of the substituted cyclic compound; and

(c) further activating the substituted cyclic compound to release the guest from the substituted cyclic compound; the substituted cyclic compound characterized in that it includes:

(i) a cyclic structure having a cavity possessing a size and shape to include a non-covalently bound guest molecule; and (ii) at least one substituent chemically bonded to said cyclic structure, said substituent, upon activation, reacting with said cyclic structure or with another substituent to form a bridge which at least partially blocks access to said cavity of said cyclic structure.

18. A complex, comprising:

(a) a substituted cyclic compound useful in the reversible entrapment of a guest, including:

(i) a cyclic structure having a cavity possessing a size and shape to include a non-covalently bound guest molecule; and

(ii) at least one substituent chemically bonded to said cyclic structure, said substituent, upon activation, reacting with said cyclic structure or with another substituent to form a bridge which at least partially blocks access to said cavity of said cyclic structure; and (b) a guest molecule trapped within said cavity.

19. A complex, comprising:

(ii) at least one substituent chemically bonded to said cyclic structure, said substituent forming a bridge which partially blocks access to said cavity of said cyclic structure, thereby preventing release of a guest molecule from said cavity.