In this work we present the first attempt of modelling the deuterium chemistry in the massive young protostellar core NGC 2264 CMM3 .
We investigated the sensitivity of this chemistry to the physical conditions in its surrounding environment .
The results showed that deuteration , in the protostellar gas , is affected by variations in the core density , the amount of gas depletion onto grain surfaces , the CR ionisation rate , but it is insensitive to variations in the H _ { 2 } ortho-to-para ratio .

Our results , also , showed that deuteration is often enhanced in less-dense , partially depleted ( < 85 % ) , or cores that are exerted to high CR ionisation rates ( \geq 6.5 \times 10 ^ { -17 } s ^ { -1 } ) .
However , in NGC 2264 CMM3 , decreasing the amount of gas depleted onto grains and enhancing the CR ionisation rate are often overestimating the observed values in the core .
The best fit time to observations occurs around ( 1 - 5 ) \times 10 ^ { 4 } yrs for core densities in the range ( 1 - 5 ) \times 10 ^ { 6 } cm ^ { -3 } with CR ionisation rate between ( 1.7 - 6.5 ) \times 10 ^ { -17 } s ^ { -1 } .
These values are in agreement with the results of the most recent theoretical chemical model of CMM3 , and the time range of best fit is , also , in-line with the estimated age of young protostellar objects .

We conclude that deuterium chemistry in protostellar cores is : ( i ) sensitive to variations in the physical conditions in its environment , ( ii ) insensitive to changes in the H _ { 2 } ortho-to-para ratio .
We also conclude that the core NGC 2264 CMM3 is in its early stages of chemical evolution with an estimated age of ( 1 - 5 ) \times 10 ^ { 4 } yrs .