SOLID SURFACE FOR PEPTIDE SYNTHESIS

Abstract: There is disclosed a solid surface, such as the surface of a rod or pin, for use in the synthesis of polymeric compounds such as peptides. The surface comprises an active region and an inactive region being positioned such that, in use, it is below the surface of the reaction liquid in a reaction well, irrespective of minor variations in liquid levels between various wells so as to eliminate the formation of deletion compounds. There are further described such surfaces for the formation of relatively large quantities of compound wherein the active region has a higher surface area/volume ratio than that of a cylinder of corresponding volume.

Description: "SOLID SURFACE FOR PEPTIDE SYNTHESIS" This invention relates to a solid surface for the synthesis of peptides thereon, and in particular relates to a rod or pin having a surface on which a peptide may be synthesized efficiently and economically. In prior International Patent Specification No. PCT/AU84/00039, there is disclosed a method for the simultaneous synthesis of a large number of different peptides. Basically, this method involves the synthesis of peptides onto a solid polymeric surface, such as polyethylene, which is molded into the shape of a rod or pin. In a preferred embodiment of the method (but not limited to it), these rods or pins are positioned in a holder so that they form a 12 by 8 matrix, with the rods or pins being positioned so that the spacing corresponds to that of the wells of microtitre plates which are widely used for ELISA (enzyme-linked immunosorbent assay) tests. The method disclosed in this prior specification was based on the realization that for the solid-phase synthesis of any peptide, almost all of the steps of the synthesis are exactly the same for any peptide and are independent of the sequence of the peptide being synthesized. Thus, with the rods or pins arranged in the preferred format so that 96 are in a holder, all steps in the synthesis such as washing steps, neutralization steps and deprotection steps can be carried out simultaneously in the synthesis of 96 different peptides. The only steps which must be carried out separately for each disregarded. In another example, the portion providing the active region could be manufactured by sintering together spherical particles of glass, ceramic or other suitable materials. Furthermore, the remaining portion providing the inactive or support region may be constructed of a material selected solely for its mechanical properties and which may not be suitable at all for peptide synthesis. By way of example, this portion may be constructed from polypropylene or some other non-porous plastic material. Secondly, the surface of the portion providing the active region will usually need to be treated to enable peptides or other polymers to be synthesized on to its surface. One suitable method disclosed in International Patent Specification No. PCT/AU84/00039 involves the grafting of polyacrylic acid onto the surface of a solid polyethylene support using gamma-irradiation. Dividing the rod into two functional portions - one providing the active region and another providing the inactive or support region also ensures that syntheses are more controlled. If the active region is the only component of the system which has been treated to allow synthesis of the peptide or other polymer, then synthesis will be restricted to it and it alone, in contrast to the earlier system, in which the complete rod was grafted with polyacrylic acid. In that earlier system, the region on the rod on which peptide was grafted was completely defined by the volume of reagent used for the coupling of specific amino acids to the growing peptide, or more accurately, the depth into which the rod dipped into the amino acid solutions. As this depth inevitably varied slightly from cycle to cycle in the synthesis, the result was a small region on the rod where the peptide synthesized may have had appreciable amounts of deletion peptides (that is, peptides whose sequence varied from that intended by having one or more residues absent) portion) . It will be apparent that the surface area of the active region of the rod can be further increased by further modification of its geometric shape, and equally that such modifications can be made by molding the rod in its final desired shape or by machining a molded rod into its final desired shape. However, in a preferred embodiment of the invention, the portion providing the active region of the rod is made by joining small particles of solid materials together, for instance, by sintering using pressure or heat or both. This can be particularly useful where it is desired to use particular harsh chemistries or virulent solvents. For instance, glass is resistant to most solvents which would make most conventional plastic materials unstable. Thus an active region could be made by sintering together small spherical beads of glass. This could then be treated, for instance, by functionalizing the surface with an amino-silane, to make it suitable as a base on which the peptide or other polymeric compound could be synthesized. In this example, the inactive region would be made from a particularly resistant plastic such as polytetrafluoroethylene. In this way, a material such as glass, which would be an unsuitable material for the inactive region, can be used with advantage in the active region. A further advantage of this particular embodiment of the invention is the large increase in the surface area/volume ratio of the active region can be achieved. Using the example given above, 8885 spherical rigid particles each with a radius of 0.1 mm would occupy the volume of the portion providing the active region of the rod if close packed together. The surface area of these spheres would be 1116.4 mm 2 , 17.8 times the surface area of a solid cylindrical portion. Decreasing the size of configurations for the "tip" portion of the rod or pin which may be separately manufactured and treated to provide the active region. In (b), there are shown both the longitudinal section (along the line A-A) and cross section (along the line B-B) of one configuration which provides a "vaned" tip. In (c), there is shown in longitudinal section a more simple tip configuration which may, for example, be either a solid plastics tip or a molded tip made up of sintered small particles. Further features of the present invention are illustrated, by way of example only, in the following example. EXAMPLE 1 10000 of. the "vaned" tips illustrated in Figure 3(b) (with an external diameter of 5 mm) were gamma-irradiated in 1 litre of 6% acrylic acid solution as described in International Patent Specification No. PCT/AU84/0003 . The tips then had hexamethylenediamine (HMD) coupled to the grafted polyacrylic acid by exposing them to a solution of 36.48 g t-butoxycarbonyl-hexamethylenediamine HCl, 24 ml triethylamine (TEA), 30.95 g dicyclohexylcarbodiimide (DCC), and 23.33 g 1- hydroxybenzotriazole (HOBt) in 1.2 L of dimethylformamide (DMF) . The tips were then washed and deprotected using the usual methods. A proportion of the free amine groups on the tips were coupled to β-alanine by exposing the tips to a solution containing 26.19 g 9- fluorenylmethoxycarbonyl jβ-alanine, 17.07 g DCC, 25.27 g HOBt, and 3.56 g diisopropylethylamine in 1.37 L of DMF. After washing, the tips were assembled on their shafts and positioned in 12 x 8 matrices. By contrast, 10000 of the rods or pins illustrated in Figure 1 were gamma-irradiated to graft polyacrylic acid to their entire surface using the earlier method disclosed in International Patent Specification No. PCT/AU84/00039. Because of the greater bulk of the complete rod or pins, 11 L of the acrylic acid solution was required. After grafting, the rods or pins were assembled in 12 x 8 matrices and HMD coupled to the spherical tip of the rods. 1.2 L of solution as described above was prepared and dispensed in 150 μL quantities into microtitre trays. The rods were then inserted into this solution. This quantity was sufficient to couple HMD to 7230 rods. After washing and deprotection in the usual manner, B-alanine was coupled to the free amine groups using 735 mL of the solution described above. This quantity was sufficient to couple 4608 rods or pins. The amount of free amine groups on the tips after coupling with HMD was 2230 nmole/tip whereas it was 1015 nmole/pin for rods or pins treated in the earlier way as disclosed in International Patent Specification PCT/AU84/00039. This difference in free amine level reflected the greater surface area of the "vaned" tips. This example also illustrates that use of the invention allows more active regions to be made at one time without the need to use more reagents and without the need to individually dispense reagents. The hexapeptide, EYYLNH (using the single letter code to represent the amino acid residues in the hexapeptide), was synthesized on to 8 of each the rods or pins described above. This synthesis was carried out using the standard Fmoc chemistry for solid-phase synthesis of peptides. The peptides were then assayed in a standard enzyme-linked immunosorbent assay (ELISA) using an antibody which specifically reacted with the peptide. The active regions synthesized according to the invention gave a mean absorbance of 2.55 with a standard deviation of 0.104 (coefficient of variance = 4%). By contrast, rods or pins treated in the earlier way as disclosed in International Patent Specification No. PCT/AU84/00039 gave a mean absorbance in the ELISA of 1.17 with a standard deviation of 0.116 (coefficient of variance = 10%). This example illustrates the advantage of processing the active region of the rod or pin separately from the inactive region in substantially reducing rod-to-rod variation in testing. It will be appreciated that many modifications and variations may be made to the specific embodiments described herein without departing from the broad principles of this invention as described herein, and all such modifications and variations are included within the ambit of this invention.

Claims: The claims defining the invention are as follows: 1. A solid surface for use in the synthesis of peptides or other polymeric compounds thereon, which surface comprises an active region on which said synthesis may take place and an inactive region on which said synthesis will not take place. 2. A solid surface of claim 1 wherein the surface is the surface of a rod having a portion providing the active region and remaining portion providing the inactive region. 3. A solid surface of claims 1 or 2 wherein the geometry of the active region is modified to provide a change in the surface area to volume ratio of the active region. 4. A solid surface of any one of claims 1 to 3 wherein the active region and the inactive region are manufactured as separate entities and then combined or assembled before use in the synthesis of peptides or other polymeric compounds. 5. A solid surface of claim 4 wherein the active region and the inactive region are manufactured by different processes or manufactured from different materials. 6. A solid surface of claims 4 or 5 wherein the active region is formed by coalescing or sintering together a large number of smaller solid particles. 7. A solid surface for use in the synthesis of peptides or other polymeric compounds thereon, which surface comprises an active region which is of a higher surface area/volume ratio than that of a cylinder of corresponding volume. 8. A solid surface according to Claim 7 wherein the active region comprises a porous material. 9. A solid surface according to Claim 7 or 8 wherein the active region comprises a plurality of relatively small particles joined together. 10. A solid surface substantially as herein described with reference to the examples and accompanying drawings.

Inventors: GEYSEN HENDRIK MARIO, GEYSEN, HENDRIK, MARIO
Applicants: COSELCO MIMOTOPES PTY LTD, COSELCO MIMOTOPES PTY LTD.
Application year: 1990
Main classification: C07K1
IPC codes: B01J19, C07K1, C40B40