1. Field of the Invention
This invention relates to a process for obtaining .alpha.-L-aspartyl-L-phenylalanine, in particular, by hydrolyzing alkyl esters of .alpha.-L-aspartyl-L-phenylalanine. Certain alkyl esters of .alpha.-L-aspartyl-L-phenylalanine are well known for their usefulness as sweetening agents.
2. Description of Prior Art
.alpha.-L-aspartyl-L-phenylalanine is a precursor material in a process for the preparation of certain alkyl esters of .alpha.-L-aspartyl-L-phenylalanine which is described in U.S. Pat. No. 3,933,781 issued to Bachman, Oftedahl and Vineyard on Jan. 20, 1976. Copending Application Ser. No. 754,297 filed Dec. 27, 1976 also describes a process to prepare certain alkyl esters of .alpha.-L-aspartyl-L-phenylalanine in which .alpha.-L-aspartyl-L-phenylalanine is involved in forming the ester.
In the process of U.S. Pat. No. 3,933,781 .alpha.-L-aspartyl-L-phenylalanine is subjected to esterification with an alkanol to form the desired ester according to the following reaction: ##STR1##
When R in the above reaction is methyl the product formed is .alpha.-L-aspartyl-L-phenylalanine methyl ester (hereinafter referred to as .alpha.-APM) which is well known for its usefulness as a sweetening agent. For convenience, .alpha.-APM will hereinafter be used as an example of the type of ester which is formed in reaction 1) above. It is to be understood that .alpha.-APM is used for illustrative purposes and is not to be construed as a limitation of this invention.
To obtain .alpha.-APM in substantially pure form, various separation and purification steps are described in U.S. Pat. No. 3,933,781. For instance, after .alpha.-L-aspartyl-L-phenylalanine undergoes esterification according to reaction 1) it is usually desirable to separate the .alpha.-APM from the following undesired by-products which are also produced during the esterification reaction: ##STR2## (hereinafter referred to as the "aspartyl ester"), R in the above structures being methyl when preparing .alpha.-APM.
The term "alkyl esters of .alpha.-L-aspartyl-L-phenylalanine" when used herein encompasses the aforementioned several forms of esters which are formed during the esterification of .alpha.-L-aspartyl-L-phenylalanine. Specifically, the term encompasses the desired ester form shown in reaction 1), diester and aspartyl ester.
The separation and purification steps to obtain .alpha.-APM in substantially pure form are difficult due to the similarity of materials present. Complete separation is often not possible, resulting in incomplete recovery of the .alpha.-APM during these separation and purification steps.
The production of undesired esters and incomplete recovery of the .alpha.-APM in separation and purification steps result in lower overall yields in a process to produce .alpha.-APM. It is therefore desirable to provide efficacious recovery methods to improve the economics of the process.
It is an object of this invention to provide a method for obtaining .alpha.-L-aspartyl-L-phenylalanine from alkyl esters of .alpha.-L-aspartyl-L-phenylalanine. The .alpha.-L-aspartyl-L-phenylalanine could then be recycled to produce .alpha.-APM according to reaction 1). The advantages of reduced waste and yield improvement are apparent to one skilled in the art.
Further objects, aspects and advantages of this invention will be apparent from the description and claims which follow.